Agreed --- some things seem normal after you've gotten used to them, whereas from another perspective, almost everything in our packs could seem odd to someone with no backpacking experience.

I'll start, nevertheless. I carry a couple of bread bags, i.e., the plastic bag that a loaf of sort of standard sliced bread comes in. Get the food smell off it, of course.
Why carry these? I have just one pair of hiking footwear, quick drying (but quick to get wet) trail runners. If it's wet (and possibly cold) then when I setup camp I change into dry socks and put the breadbags over them to keep the wet shoes from getting the socks wet. In unusually cold weather they double as a poor man's VB (vapor barrier) socks.

Okay, here's another one --- use a snow/sand stake (a single one) in lieu of a trowel. Not as good as a real trowel, but it's light, and doubles as a good soft-soil tent stake (or just spare tent stake) when needed.

How about small squares of ccf to put into the backs of socks for colder nights? I.e., increase the effective thickness of insulation at the backs of heels.