Work on creating more of the necessary data models

module/models/Item/CommonItemData.mjs

@@ -1,11 +1,22 @@
+import { itemTiers } from "../../config.mjs";
+
 export class CommonItemData extends foundry.abstract.TypeDataModel {
 	static defineSchema() {
 		const fields = foundry.data.fields;
 		return {
-			cost: new fields.NumberField({
+			buy: new fields.NumberField({
 				initial: null,
 				nullable: true,
 			}),
+			usage_cost: new fields.NumberField({
+				initial: null,
+				nullable: true,
+			}),
+			tier: new fields.StringField({
+				initial: `simple`,
+				nullable: false,
+				choices: itemTiers,
+			}),
 		};
 	};
 };

module/models/Item/Equipment.mjs

@@ -0,0 +1,15 @@
+import { DescribedItemData } from "./DescribedItemData.mjs";
+
+export class EquipmentItemData extends DescribedItemData {
+	static defineSchema() {
+		const fields = foundry.data.fields;
+		return mergeObject(super.defineSchema(), {
+			extra_inventory: new fields.NumberField({
+				initial: null,
+				nullable: true,
+				required: false,
+			}),
+			material
+		});
+	};
+};

module/models/Item/Pet.mjs

@@ -4,7 +4,6 @@ export class PetItemData extends DescribedItemData {
 	static defineSchema() {
 		const fields = foundry.data.fields;
 		return mergeObject(super.defineSchema(), {
-			purchase: new fields.NumberField({ initial: 0, }),
 			upkeep: new fields.NumberField({ intial: null, nullable: true }),
 			pokeballd: new fields.BooleanField({ initial: false }),
 		});

module/models/Item/Transportation.mjs

@@ -8,10 +8,6 @@ export class TransportationItemData extends DescribedItemData {
 				initial: null,
 				nullable: true,
 			}),
-			purchase: new fields.NumberField({
-				initial: null,
-				nullable: true,
-			}),
 			upkeep: new fields.NumberField({
 				initial: null,
 				nullable: true,