Vise-Grip wrench - I've got maybe a dozen of them and they are awesome. They come in handy as an extra hand to clamp things to the table or to tie some rope to it and lash something down, or just to use as a regular wrench in a pinch. They come in all sizes, but I prefer the regular size and the super big size for plumbing and dogging. For awhile I was considering getting the Leatherman Crunch, which is a vise-grip version of their plier-tools. I still might one day, as I seriously lament not having one around with me often. It's hard to find room for two multitools in one pair of pants, though. I keep one in my motorcycle tool kit as it can hold most of the bike together by itself should any bolts fall off.
Bic adjustable cigarette lighter - these are much more resistant to breakage than the translucent cheapo models, and they are good for so many things around the house and camping and seeing in the dark, fixing things, available everywhere, cheap, and last forever.
90-second/5-minute epoxy - I keep a tube of this at the lab and have epoxied everything from liquid nitrogen tanks to fluorescence spectros to dog crates with it. It stinks, and is inflexible when set, but there is absolutely no room for superglue in my world since this came along. You get so much more for the price, and it's quick-setting (sometimes too quick).
Tony Chachere's original creole seasoning - I know, it's not a 'tool' per se, but listen to me on this one. If you put this stuff on your food, and some gets on your hand, you run the risk of eating the hand. It will make a bowling ball edible. It's got everything blended in it, and it's cheap. Maybe it's harder to find up north, but he's got a website where you can order it and open a brand new refulgent chapter of your life. I suppose you could use it to melt iced up sidewalks or to clear out your sinuses (it's spicy), but it's the ultimate food ubertool (along with McIlhenny's Tabasco sauce, of course).
100% cotton white handkerchief - I used to carry these things religiously. I started to receive some polyester/cotton mix ones for Xmas some years ago, and they were so god-awful that it kind of messed up my whole snot-rag carrying habit. I need to force myself back into it regularly, as these things are perfect for wiping oil and sweat off of your face, and serving as a surrogate paper towel in a shitty men's room (or god forbid, as toilet paper), or to blow your nose, or to put your face on if you have to sleep on the floor or dirt (this is a handy use), and they'll sop up a spilled coke or wipe off an unclean fork with ease. What else are you going to put in your lonely left back pocket, I ask you? A pack of 4 costs like 4 bucks so use and toss if you mess them up too badly. My friend Alex carries those big bandanas instead, but while they are better for some things, they are just not as absorbant or nearly as comfortable. And they look absolutely absurd in your pocket unless you're a rodeo clown.