A couple of rolls of wax paper to protect clamps and tables when doing glue-ups
A roll of paper towels I use for many purposes. Mostly for applying wipe on finishes and rubbing those finishes. I use for cleaning dust off of surfaces to be finished. Just about anything I would use a piece of cloth for wiping or cleaning. I am never tempted to try to save a used paper towel like I might a used rag. And it is far tougher than I thought before first I ever used for wipe-on finishes.
Old fireplace bellows. I use for blowing dust out of corners where my vac hose won't reach. It doesn't suck dust, but with judicious directing, it gets the dust closer to the vac and i don't have to move machinery around so i can get closer with my vac. There's also a funny little story I am reminded with every use involved with the bellows. (still unwritten, but in my head for nearly 50 years. That one involves my MIL who is long gone)
Pencils in many corners and drawers. I never can find the pencil I am using. I gave up trying to develop the habit of keeping close to where I am using or in my pocket long ago. I just don't spend a lot of time looking as I know the pencil I have misplaced will turn up some where, some time. If i mislay, i just open a drawr and there is a pencil. If i find one lying around, i just stick in a drawer or put on a horizontal surface where it can be seen.
Ear muffs. They block out machinery noise so I can listen to the crickets and katydids.
Disposable gloves have been mentioned. I don't keep them in the shop. I raid The BOSS'S supply.
Velcro. I have several different widths. That stuff comes in handy for many more times than I ever dreamed.
Used tooth brushes. I use mostly for cleaning tools, especially for cleaning router bits.
Tinker