26 CFR § 1.471-1 - Need for inventories.
In order to reflect taxable income correctly, inventories at the beginning and end of each taxable year are necessary in every case in which the production, purchase, or sale of merchandise is an income-producing factor. The inventory should include all finished or partly finished goods and, in the case of raw materials and supplies, only those which have been acquired for sale or which will physically become a part of merchandise intended for sale, in which class fall containers, such as kegs, bottles, and cases, whether returnable or not, if title thereto will pass to the purchaser of the product to be sold therein. Merchandise should be included in the inventory only if title thereto is vested in the taxpayer. Accordingly, the seller should include in his inventory goods under contract for sale but not yet segregated and applied to the contract and goods out upon consignment, but should exclude from inventory goods sold (including containers), title to which has passed to the purchaser. A purchaser should include in inventory merchandise purchased (including containers), title to which has passed to him, although such merchandise is in transit or for other reasons has not been reduced to physical possession, but should not include goods ordered for future delivery, transfer of title to which has not yet been effected. (But see § 1.472-1.)