I include more of what I need of some goods, partly so that I have a surplus I can give to others. Example goods include toilet paper, rice, even water.

Alcohol is an interesting one because I don't consider it to preparedness item in the normal sense, of something I'd need for my own survival. I do stockpile it as a potential barter item, but I probably wouldn't bother if I didn't also drink it in normal life.

Everything kept needs to justify its place, and the most useful things for barter are going to be the things useful in themselves, so nothing is really kept purely for barter. And it's hard to predict what other people will want; most likely it will be the same things I want. You can hope to get lucky with consumables that often get overlooked, but you never know what there will be shortages of. Partly I am driven by convenience. Toilet paper is convenient for me because it doesn't expire.