The technical terms used the Uniform Commercial Code (a law adopted in all U.S. states), which describes the rights of the buyer and seller when merchandise has been sold and is awaiting shipment are "identified goods" and "sold goods" (Article 2, Sections 105, 401, 402 and 704).
Ultimately Richard Kayser's intuition of "sold" isn't a bad one although usually "sold", alone, is used as an adjective rather than a noun (in the case where there is a tag on the goods the adjective is modifying a physical object which is a noun, rather than a word which is a noun; there is probably a fancy word for that too).
A less technical term would be to refer to the merchandise as "your purchase" (although this describes the merchandise both before and after it is picked up by the buyer). You could also call it a "package" ("a commodity or a unit of a product uniformly wrapped or sealed" per Merriam-Webster), a "parcel" ("a wrapped bundle" or "a unit of saleable merchandise" per Merriam-Webster), a "shipment" ("the goods shipped" per Merriam-Webster), or an "order" (a "product that a customer has asked for" per MacMillian Dictionary) .
Amazon.com uses terms such as "orders", "open orders" ("An order that has not been executed and remains in the system available to be filled until an order to cancel it is received." per InvestorGuide.com), and "packages" in its logistics process. A package or parcel or shipment could be at any state of the delivery process, but an "order" or "open order" is quite close to the mark.
Perhaps even better in terms of precision (although often used for intangible goods in the context of project management, rather than for merchandise in a more general sense) is a "deliverable" ("a tangible or intangible product or service produced as a result of the project that is intended to be delivered to a customer" per Wikipedia).
"Freight" ("goods carried by a large vehicle" per Synonymn.com) seems like more merchandise than you are talking about.
Less technically, someone at a store would say that merchandise is "on hold" for a customer ("to set aside, reserve, retain" per Dictionary.com), although usually this would be a situation that precedes an actual sale, rather than a term applied to purchased goods.
An international treaty called the C.I.S.G. that handles the sale of merchandise in where the buyer and seller are in different signatory states calls merchandise "specific goods" in this situation. (C.I.S.G. Article 31(b)), although it also describes them as "identified goods" (e.g. C.I.S.G. Article 67).
Another related concept is "special property" (Uniform Commercial Code, Article 2, Section 501, 502, 716 and 722) which merchandise becomes when it is "identified", but this meaning isn't widely known beyond specialists in commercial law.
Before the goods are sold, of course, the goods are usually "inventory" (i.e. merchandise owned by someone in the business of selling merchandise per Wikipedia) or "stock" (same source), and "sold inventory" or "identified inventory" would be a valid alternative to sold goods.
Another technical term for the state of being in possession of personal property such as merchandise without actually owning it (when there is no intent to sell it to third parties) is a "bailment" (per Wikipedia), but while the situation has a technical name, there is not as widely used a term for the property that is subject to the bailment.
A less technical term is that good are held on "layaway" (a.k.a. "lay-by" in British English), per Wikipedia, and have been paid for. In this arrangement a sale in exchange for installment payments is made but the seller retains possession until the entire price is paid and sometimes longer until the buyer is ready to take delivery.
A related concept is a sale "F.O.B. seller's shop" (Uniform Commercial Code, Article 2, Section 319) which means that the goods are "free on board" with title and responsibility transferring to the buyer at the point of the seller's shop. (F.O.B. can be followed by any location and is sometime used confusingly without clarifying where the goods are "F.O.B.").
A "bill of goods" does not quite have the meaning you suggest, and is derived from a "bill of sale" (i.e. a document that is equivalent to a deed for real estate that actually transfers ownership of the goods at the moment it is signed per Wikipedia). You've received a "bill of goods" when you are given a "bill of sale" transferring the goods to you, but not the actual goods themselves.
"Consignment" (Uniform Commercial Code, Article 2, Section 326) means an arrangement in which the person possessing and offering to sell a good is not its owner, as opposed to the usual case when a seller buys inventory that becomes the property of the seller and then offers it for sale. The word "Consigned" means delivered to or shipped, and is a verb, per Dictionary.com.