I was thinking just know about how I have listed a few choice items that I give "ubertool" or something like this status due to their unparalleled usefulness/handiness. The list as I can remember right off the top of my head is:
multi-tool (I've preferred leatherman wave for years now, but of course it has its downsides). It must have a knife blade, pliers, file, and both types of screwdrivers to be at all useful to me, but preferably with wire-cutters and an awl-shaped tool also. I use mine so often I dulled the blade in a month and I would rather leave my wallet at home than my leatherman. I originally got a leatherman (the only one they made at the time" when I was a kid and it was awesome, though light on features. Then I got a Wave I when my dad died because the engraved original was too important to lose or break, and it worked well. Then I got a Charve XTi, and it was a waste of money. The handle was waaay too bulky (what's the point of titanium if the thing's going to be so big and heavy otherwise?), and although the blades were supposedly better quality, I didn't notice any difference (though the shape was better). I liked the shape of the pliers over the wave, but the screwdriver scenario was not cool with me (two philips-heads instead of scissors? unacceptable). Eventually I lost it because it was too heavy to stay in my pocket correctly. I got a "new wave" which is essentially the old one with their new interchangeable bit set. The knife blade is rather easy to dull, but, sharpenable. A great review of multitools (and where I got a lot of the advice for building my custom first-aid kits is at http://www.equippedtosurive.org .
tape (of course duct tape is the king, but not all duct tape is created equally, and the size of the roll is a trammel. I'm starting to test the usefulness of the standard cloth coach's/medical tape for the same purposes as it's smaller, and usually pretty sticky & strong). I've been wanting to try that '100 mile per hour tape and also gaffer's tape, but I dunno where to get some to try it. Besides, medical tape/duct tape is more ubiquitous.
clear nail polish (this stuff is cheap and works as waterproofer, seam sealer, wound closer, clear-coat, rust-protector, lubricator, glue, and scratch remover among other things), and they sell it everywhere that women live and it's only a couple of bucks, and the bottles are indestructible.
Ultra-fine-tip sharpie blue as it is by far the most durable ink color for some reason, and very visible for my work, the cap stays on tightly, it lasts a long time, the clip doesn't bend, and it writes on anything
Pilot Precise V5 pen because it's bold colored, doesn't need ink priming, etc. It has drawbacks (bleeds easy, crushes easy, can be messy) but my fav usually
Five new $1 bills because with these things you can get just about ANYTHING done easier. Plus they buy me my daily diet sodas at work in the morning.
Visa/Mastercard because with this you can do anything the cash won't get you. And it can open most doorknob locks in old buildings, and scrape nasty shit off of your car and desk without using your pocketknife.
One sheet of notebook paper folded 3 times will hold all to-do lists, to-call lists, and any info you pick up along the day, along with random doodles and whatnot. I have a shelf of my bookcase where I've been keeping these things since college, and when I'm bored I look through them to see what was going on back then. Screw that PDA nonsense.
Anyway if there are other suggestions for ubertools or comments, please let me know, and I will be updating this list as I think of new ones.