In no particular order, consider accumulating some of the following items for barter purposes. And keep in mind that in a post-collapse world, the items do not necessarily have to be new, but simply serviceable.
Water purification supplies including purification tabs and filters
Hand tools including hatchets, saws, machetes and general fix-it tools
Fire making supplies, including lighters, matches, flint fire steel
Sanitary supplies including toilet paper, feminine products and diapers
Disposable razors and razor blades
Fuel, any and all kinds (gas, diesel, propane, kerosene)
Prescription drugs, painkillers, and antibiotics
First aid remedies such as cough syrup, cortisone cream, boil-ese, calamine lotion and topical pain relievers
Spirits such as bourbon, rum, gin, and vodka
Coffee and tea (instant coffee is okay)
Solar battery charger and rechargeable batteries
Standard Batteries
Reading glasses
Paracord
Bags, including large garbage bags as well as smaller zip-close bags
Plastic sheeting
Duct tape
Tie Wraps
Heavy plastic sheets and tarps
Toiletries including toothpaste, dental floss soaps, shampoo (tip: save those small sized toiletries that are provided by hotels and motels)
Condoms
Latex or Nitrile gloves in a variety of sizes
Hard candy
Fishing supplies
Knives of various types including fixed blades, kitchen knives, and box cutters.
Condiments and Spices
Paperback books on a variety of subjects
Tobacco and cigarette rolling supplies
Amusements such as playing cards, crossword puzzle books, Sudoku
Pencils & paper
Pepper spray
Garden seeds
Flashlights
Vinegar and baking soda to use in DIY cleaning supplies
Empty spray bottles and squirt bottles
Hand pumps for both air and liquids
Mylar blankets and tents
Hand warmers
Sewing and mending supplies
Knitting or crochet needles and Yarn
One thing you will notice that I have not included firearms or ammo and for good reason. In a post-collapse society, you might not know your barter partners well and may run the risk that they will use these items against you so that they can steal the rest of you stuff. One person’s opinion, anyway.