Gold and Silver
I have seen calipers recommended for testing that the size of your coin or bar is what it should be. For coins it would seem easier to use a calibrated beaker or some such and to know how much volume a coin should displace.
Also, I read that gold is weighed in Troy ounces, a troy ounce being 1.09714 “normal” ounces. And you will want to be able to Test Gold or Silver for Authenticity
Buy green coffee beans and a Whirly-Pop popcorn popper. The coffee beans are actually the seeds of the coffee tree. They will get stale for probably several years, and so you can roast them up as needed to consume your own fresh coffee or barter with it. The Whirly-Pop is a hand crank unit that will roast beans over any cooking heat. To ensure quality, buy beans that were grown on a single, specific plantation. Don’t buy beans that are generally from a region, as these will not be as good a quality. Experiment.
Any tobacco will make good barter stock. Vacuum pack it if you can.
I don’t know the current shelf-life of bullets or gunpowder.
Any sweets will be potential barter material. Sugar is addictive and folks will be craving it.
I am Mr. Natural. What do I know about medications? Aspirin? Cayenne and garlic equals penicillin. You can grow them and barter them if you include usage instructions.
Livestock and Produce
See my Homestead and Tiny Homestead pages to learn about ways to grow stuff!
Sell your Antiques – maybe not a barter item, but you may have antiques to unload before committing to the homestead life.