Barter has been mentioned in a couple of threads recently. I wanted to take a try at it and I have the time, layed up with a pinched nerve.
I look for items that are inexpensive now, will be needed later and that I can use if needed. Long or indefinite shelf life and don't take up a lot of space. Of course, if you have a lot of space there are more options. I don't smoke or chew and don't have a clue on storing those items, so I'll stay away from them.
Bartering guns & ammo that can come back to hurt you and alcohol that can lead to problems is almost it's own topic. These items deserve some special consideration. For example I probably wouldn't trade ammo with a stranger. But I'd trade with my neighbor for fresh vegetables from his garden. Don't want to be dealing with drunks or alcoholics that are in bad shape, that's just asking for trouble.
Dollar Stores, Harbor Freight (use the coupons and free items), garage sales, thrift stores and samples are all good places to procure what you want at low cost. Here some items to consider.
BBs and pellets, TP, feminine hygiene, BICs, matches. Zippo fuel, wicks, flints, bargain Zippos, canning jars, rings and tools, reading glasses, glasses repair kits. Sewing, fishing items, candles, batteries, manual can openers, work gloves, OTC meds, vitamins, FAK stuff, hand sanitizer, floss, tooth brushes, travel size pers hygiene, low cost knives and tools. Stove fuel, seeds, nails, wire, hardware. Coffee, spices, 1 LB containers sugar and salt.
If you have more space and all ready have enough for yourself, then bulk basic foods would work. Rice, beans, pasta, peas, flour, corn meal, baking basics are easy to break down into small amounts.
We mentioned skills in another thread. Medical/Dental, sewing/knitting/quilting, gardening, small animals, solar or the ability to purify water all come to mind. Very few people can do everything, so your Mutual Aid Network should include a cross section of skills. Don't forget to include the wives and GF's.