Chopsticks saved from a Chinese restaurant.
Trash-compactor bag (raincoat, mini ground tarp, and, hey, even a trash bag).
A square of wax paper as a fire starter.
Likewise, small squares of waxed, corrugated cardboard boxes (they contain produce and can be found behind your local grocery store) as fire starters.
Heat-sealed soda straws to hold pills, vaseline-impregnated cotton balls, and spices.
6" x 24" of heavy-duty aluminum foil as a wind screen.
Free, professional samples of anti-itch, antibiotic, sunscreen, etc, lotions.
Super-mini toothpaste tubes from Chinese hotels (not counting the airfare).
Scrap of copper wire, bent into a U, and hammered flat on the ends to use as a heat conductor for a butane canister.
Found-on-the-beach bits of Spectra and woven dacron fishing line, 60- to 120-pound test, cut into guy-line and emergency-shoe-lace lengths.
The smallest bit of vac-pac bag material to make pills, emergency TP, etc, super water-proof.
Cut-off bottom 1/3 of a gallon milk jug as a SUL bowl, sink, bucket and water scoop.
Dumpster-diving at the recycling center for Foster's, energy drink, and other interesting sizes and thicknesses of aluminum containers as multipurpose pots and water bottles.
Old, wide-mouth Avian bottles. Wish I could still find them. So now I use. . . .
Gatorade bottles - lighter and infinitely cheaper than Nalgene.