Some camps hold that as fiat currency will fail quickly, trade would continue for a short time in precious metals, particularly commonly minted coins. After a prolonged period of widespread supply deficiencies, those who have consumable supplies will be less inclined to part with them for non-consumables of any sort. Labor and material exchange would become the common trade commodities until some form of regulation took over. A gradual return to some monetary standard would be necessary in the long run to accommodate logistics and accounting.

Tobacco and prescription drugs; there will always be a viable market for these, and at a premium. A connex full of cartons of smokes would be a tremendous fortune in a grid-down scenario, provided one could keep it secured. A case of oxycodone or vicadin would be like owning a silo full of grain.

Agreed. Anything we identify as good, others may do the same leading to a glut of those items. It's probably better to have spare supplies of the things you want for yourself, than to use the space/money/weight for something you hope others will want.

A lot also depends on the nature of the disaster. Spare batteries might be invaluable, or they might be useless, for example.

I've done that, more or less. Not for survival, or for trade, though. It was an adventure holiday in Venezuela, with a tour guide but a "dig your own toilet" affair. We stays a few nights with a remote tribe, and were encouraged to bring gifts for them. I brought sewing needles, and they were one of the items most valued. Make-up was also appreciated.

best is to stock up on things you use. these are often the same things others want in trade.

ie: food, hygiene/medical, tools, water purifiers, clothes, building/repair supplies, fuel...

in other words: it doesn't make sense to buy/store things you aren't likely to need, just in case you wish to do some trading.