diff --git a/internal/plugin/dnd_expedition_supplies.go b/internal/plugin/dnd_expedition_supplies.go
new file mode 100644
index 0000000..2d3ac7f
--- /dev/null
+++ b/internal/plugin/dnd_expedition_supplies.go
@@ -0,0 +1,176 @@
+package plugin
+
+import (
+	"fmt"
+)
+
+// Phase 12 E1b — Supply procurement, daily burn, and depletion effects.
+// Spec: gogobee_expedition_system.md §4.
+
+// Pack pricing/yield. §4.2.
+const (
+	SupplyPackStandardSU    = 10
+	SupplyPackStandardCoins = 50
+	SupplyPackStandardMax   = 3 // per expedition
+
+	SupplyPackDeluxeSU    = 20
+	SupplyPackDeluxeCoins = 90
+	SupplyPackDeluxeMax   = 1 // per expedition
+
+	SupplyForageMaxSU = 4 // 1d4 cap (Ranger, WIS DC 12) — §4.2
+)
+
+// supplyDailyBurn returns the base SU/day for a zone tier (§4.1).
+// Tier 1: 1, Tier 2: 1.5, Tier 3: 2, Tier 4: 3, Tier 5: 4.
+func supplyDailyBurn(tier ZoneTier) float32 {
+	switch tier {
+	case ZoneTierBeginner:
+		return 1.0
+	case ZoneTierApprentice:
+		return 1.5
+	case ZoneTierJourneyman:
+		return 2.0
+	case ZoneTierVeteran:
+		return 3.0
+	case ZoneTierLegendary:
+		return 4.0
+	}
+	return 1.0
+}
+
+// supplyHarshMultiplier returns the harsh-conditions multiplier (§4.1).
+// Tier 1×1, Tier 2×1.5, Tier 3×2, Tier 4×2.5, Tier 5×3.
+func supplyHarshMultiplier(tier ZoneTier) float32 {
+	switch tier {
+	case ZoneTierBeginner:
+		return 1.0
+	case ZoneTierApprentice:
+		return 1.5
+	case ZoneTierJourneyman:
+		return 2.0
+	case ZoneTierVeteran:
+		return 2.5
+	case ZoneTierLegendary:
+		return 3.0
+	}
+	return 1.0
+}
+
+// SupplyDepletionState classifies remaining supply ratio (§4.3).
+type SupplyDepletionState int
+
+const (
+	SupplyNormal SupplyDepletionState = iota
+	SupplyRationing
+	SupplySevereRationing
+	SupplyStarvation
+)
+
+// supplyDepletion returns the depletion state for a supplies snapshot.
+// Brackets: >25% normal, 10–25% rationing, 1–9% severe, 0 starvation.
+func supplyDepletion(s ExpeditionSupplies) SupplyDepletionState {
+	if s.Max <= 0 {
+		return SupplyNormal
+	}
+	if s.Current <= 0 {
+		return SupplyStarvation
+	}
+	pct := (s.Current / s.Max) * 100
+	switch {
+	case pct >= 25:
+		return SupplyNormal
+	case pct >= 10:
+		return SupplyRationing
+	default:
+		return SupplySevereRationing
+	}
+}
+
+// supplyRollModifier maps depletion state to the universal roll penalty
+// applied to attack/skill rolls (§4.3). Starvation has its own CON bleed
+// handled elsewhere; the roll mod for starvation matches severe rationing
+// floor so combat math doesn't divide by zero.
+func supplyRollModifier(state SupplyDepletionState) int {
+	switch state {
+	case SupplyRationing:
+		return -1
+	case SupplySevereRationing, SupplyStarvation:
+		return -2
+	}
+	return 0
+}
+
+// supplyAllowsLongRest returns false when severe rationing (§4.3) blocks
+// long rests. Starvation also blocks (forced extraction is the next step).
+func supplyAllowsLongRest(state SupplyDepletionState) bool {
+	return state == SupplyNormal || state == SupplyRationing
+}
+
+// SupplyPurchase represents an expedition outfitting choice.
+type SupplyPurchase struct {
+	StandardPacks int
+	DeluxePacks   int
+}
+
+// Total SU yield from a purchase.
+func (p SupplyPurchase) Total() float32 {
+	return float32(p.StandardPacks*SupplyPackStandardSU + p.DeluxePacks*SupplyPackDeluxeSU)
+}
+
+// Total cost in coins.
+func (p SupplyPurchase) Cost() int {
+	return p.StandardPacks*SupplyPackStandardCoins + p.DeluxePacks*SupplyPackDeluxeCoins
+}
+
+// Validate enforces §4.2 caps (max 3 standard, max 1 deluxe, no negatives,
+// at least one pack purchased — an expedition without supplies is not a
+// legal start).
+func (p SupplyPurchase) Validate() error {
+	if p.StandardPacks < 0 || p.DeluxePacks < 0 {
+		return fmt.Errorf("supply pack counts must be non-negative")
+	}
+	if p.StandardPacks > SupplyPackStandardMax {
+		return fmt.Errorf("standard packs capped at %d (got %d)", SupplyPackStandardMax, p.StandardPacks)
+	}
+	if p.DeluxePacks > SupplyPackDeluxeMax {
+		return fmt.Errorf("deluxe packs capped at %d (got %d)", SupplyPackDeluxeMax, p.DeluxePacks)
+	}
+	if p.StandardPacks == 0 && p.DeluxePacks == 0 {
+		return fmt.Errorf("expedition requires at least one supply pack")
+	}
+	return nil
+}
+
+// makeSupplies builds an ExpeditionSupplies from a purchase, sized for the
+// given zone tier. Harsh-conditions multiplier defaults to 1 (off);
+// upgraded by E2/E3 events.
+func makeSupplies(tier ZoneTier, p SupplyPurchase) ExpeditionSupplies {
+	total := p.Total()
+	return ExpeditionSupplies{
+		Current:       total,
+		Max:           total,
+		DailyBurn:     supplyDailyBurn(tier),
+		HarshMod:      1.0,
+		PacksStandard: p.StandardPacks,
+		PacksDeluxe:   p.DeluxePacks,
+	}
+}
+
+// applyDailyBurn deducts one day's supplies from the snapshot (caller
+// persists). Returns the new snapshot and the SU consumed.
+func applyDailyBurn(s ExpeditionSupplies, harshActive bool) (ExpeditionSupplies, float32) {
+	burn := s.DailyBurn
+	if harshActive {
+		burn *= s.HarshMod
+		if burn == s.DailyBurn { // HarshMod was 0 / unset
+			burn = s.DailyBurn
+		}
+	}
+	s.Current -= burn
+	if s.Current < 0 {
+		s.Current = 0
+	}
+	// Reset per-day forage flag.
+	s.ForagedToday = false
+	return s, burn
+}
diff --git a/internal/plugin/dnd_expedition_supplies_test.go b/internal/plugin/dnd_expedition_supplies_test.go
new file mode 100644
index 0000000..55d3afa
--- /dev/null
+++ b/internal/plugin/dnd_expedition_supplies_test.go
@@ -0,0 +1,160 @@
+package plugin
+
+import "testing"
+
+func TestSupplyDailyBurn_AllTiers(t *testing.T) {
+	cases := []struct {
+		tier ZoneTier
+		want float32
+	}{
+		{ZoneTierBeginner, 1.0},
+		{ZoneTierApprentice, 1.5},
+		{ZoneTierJourneyman, 2.0},
+		{ZoneTierVeteran, 3.0},
+		{ZoneTierLegendary, 4.0},
+	}
+	for _, c := range cases {
+		if got := supplyDailyBurn(c.tier); got != c.want {
+			t.Errorf("tier %d: got %v, want %v", c.tier, got, c.want)
+		}
+	}
+}
+
+func TestSupplyHarshMultiplier_AllTiers(t *testing.T) {
+	cases := []struct {
+		tier ZoneTier
+		want float32
+	}{
+		{ZoneTierBeginner, 1.0},
+		{ZoneTierApprentice, 1.5},
+		{ZoneTierJourneyman, 2.0},
+		{ZoneTierVeteran, 2.5},
+		{ZoneTierLegendary, 3.0},
+	}
+	for _, c := range cases {
+		if got := supplyHarshMultiplier(c.tier); got != c.want {
+			t.Errorf("tier %d: got %v, want %v", c.tier, got, c.want)
+		}
+	}
+}
+
+func TestSupplyDepletion_Brackets(t *testing.T) {
+	cases := []struct {
+		current float32
+		max     float32
+		want    SupplyDepletionState
+	}{
+		{10, 10, SupplyNormal},        // 100%
+		{3, 10, SupplyNormal},         // 30%
+		{2.5, 10, SupplyNormal},       // 25% — boundary stays normal
+		{2, 10, SupplyRationing},      // 20%
+		{1, 10, SupplyRationing},      // 10% — boundary stays rationing
+		{0.9, 10, SupplySevereRationing},
+		{0.1, 10, SupplySevereRationing},
+		{0, 10, SupplyStarvation},
+	}
+	for _, c := range cases {
+		s := ExpeditionSupplies{Current: c.current, Max: c.max}
+		if got := supplyDepletion(s); got != c.want {
+			t.Errorf("%v/%v: got %d, want %d", c.current, c.max, got, c.want)
+		}
+	}
+}
+
+func TestSupplyRollModifier(t *testing.T) {
+	cases := map[SupplyDepletionState]int{
+		SupplyNormal:          0,
+		SupplyRationing:       -1,
+		SupplySevereRationing: -2,
+		SupplyStarvation:      -2,
+	}
+	for state, want := range cases {
+		if got := supplyRollModifier(state); got != want {
+			t.Errorf("state %d: got %d, want %d", state, got, want)
+		}
+	}
+}
+
+func TestSupplyAllowsLongRest(t *testing.T) {
+	cases := map[SupplyDepletionState]bool{
+		SupplyNormal:          true,
+		SupplyRationing:       true,
+		SupplySevereRationing: false,
+		SupplyStarvation:      false,
+	}
+	for state, want := range cases {
+		if got := supplyAllowsLongRest(state); got != want {
+			t.Errorf("state %d: got %v, want %v", state, got, want)
+		}
+	}
+}
+
+func TestSupplyPurchase_Validate(t *testing.T) {
+	cases := []struct {
+		p       SupplyPurchase
+		wantErr bool
+	}{
+		{SupplyPurchase{StandardPacks: 1}, false},
+		{SupplyPurchase{StandardPacks: 3, DeluxePacks: 1}, false}, // max
+		{SupplyPurchase{StandardPacks: 4}, true},                  // over standard cap
+		{SupplyPurchase{DeluxePacks: 2}, true},                    // over deluxe cap
+		{SupplyPurchase{StandardPacks: -1}, true},
+		{SupplyPurchase{}, true}, // none purchased
+	}
+	for _, c := range cases {
+		err := c.p.Validate()
+		if (err != nil) != c.wantErr {
+			t.Errorf("%+v: err = %v, wantErr=%v", c.p, err, c.wantErr)
+		}
+	}
+}
+
+func TestSupplyPurchase_TotalAndCost(t *testing.T) {
+	p := SupplyPurchase{StandardPacks: 3, DeluxePacks: 1}
+	if p.Total() != 50 {
+		t.Errorf("total = %v, want 50", p.Total())
+	}
+	if p.Cost() != 240 {
+		t.Errorf("cost = %d, want 240", p.Cost())
+	}
+}
+
+func TestMakeSupplies_FillsFromTier(t *testing.T) {
+	p := SupplyPurchase{StandardPacks: 2}
+	s := makeSupplies(ZoneTierJourneyman, p)
+	if s.Max != 20 || s.Current != 20 {
+		t.Errorf("supplies: %+v", s)
+	}
+	if s.DailyBurn != 2.0 {
+		t.Errorf("daily burn = %v, want 2", s.DailyBurn)
+	}
+	if s.PacksStandard != 2 {
+		t.Errorf("packs std = %d", s.PacksStandard)
+	}
+}
+
+func TestApplyDailyBurn_DrainsAndClamps(t *testing.T) {
+	s := ExpeditionSupplies{Current: 5, Max: 10, DailyBurn: 2, HarshMod: 1.5, ForagedToday: true}
+	s, burn := applyDailyBurn(s, false)
+	if burn != 2 {
+		t.Errorf("burn = %v, want 2", burn)
+	}
+	if s.Current != 3 {
+		t.Errorf("current = %v, want 3", s.Current)
+	}
+	if s.ForagedToday {
+		t.Error("forage flag should reset on day rollover")
+	}
+	// Harsh active doubles via mult.
+	s, burn = applyDailyBurn(s, true)
+	if burn != 3 { // 2 × 1.5
+		t.Errorf("harsh burn = %v, want 3", burn)
+	}
+	// Drain to floor.
+	for i := 0; i < 5; i++ {
+		s, _ = applyDailyBurn(s, false)
+	}
+	if s.Current != 0 {
+		t.Errorf("expected current clamped to 0, got %v", s.Current)
+	}
+}