Back here I talked a bit about the stuff I carry every day, and you folks left some awesome suggestions in the comments. As you might expect, my list of items changes fairly regularly as things occur to me, or as I discover things I don't need to keep lugging around. Usually a purge of my kit happens every two months or so when I get sick of all the crap I've accumulated.
But, starting from the luggage and working my way in, here's what I've been carrying every day lately:
Timbuk2 messenger bag: This thing is huge. On the Vespa, I could conceivably keep a puppy warm under the seat and have a grown beagle enjoying the breeze in my bag. Or, on the Triumph, two grown pugs in the bag. Along with my gear. Seriously, this bag is so big, it's kind of overkill. It's super easy to get on over my jacket, and it's got a cross-strap so it stays put while I'm riding.
I've abused the hell out of this bag, and it's still in great shape. I recently used it on a four mile hike, and carried water for two people, a grotesquely over-packaged lunch, my SLR and other sundries with no problem or discomfort.
Leatherman PST: While a proper, fixed blade knife would be best for survival in the backcountry, here in the urban reality most of us deal with on a day to day basis, a multi-tool is just about the best thing ever. I can't count how many times this thing has come in useful, and I'm tempted to get a collection of other multi-tools just so I can stash them in handy places.
Small flashlight: It's cheap, it's plastic, it's a source of light. I've used it several times. I gotta remember to carry spare batteries, though.
Bic Lighter Wrapped with Duck Tape: Obviously, because some times you need to make sure something stays put and then light it on fire.
...OK. So, actually, it's just a convenient way to carry several feet of duck tape. And sometimes you do need to light things on fire.
Excedrin: Best painkiller ever.
Earbuds: I like music, and when I'm going on a looooong, boring ride (say, to San Diego), it's nice to have headphones that fit under my helmet. I don't use them in traffic. They also come in handy at work when someone starts having a conversation I wish I didn't have to overhear.
Bright orange bandanna: Think about it for a minute, and you'll realize the millions of possible uses for a bandanna. Especially if you're a sweaty biker who thinks bright orange is pretty cool looking. A bandanna is just an awesome thing to have, and if you don't have one, you should really get one. Or five.
Sucrets tin full of goodies: This is an evolving kit. Presently it has a stick of chapstick, a couple bandaids, a box of matches and several safety pins. Eventually I'm going to put a few Immodium AD tablets in there, because you never know when the pizza gods might be vengeful. Future additions include a square of aluminum foil, a ziplock bag or two, moleskin, and some baling wire.
Water Bottle: I've got a bunch of these, and I rotate through them when I think of it.
Thermax thermos: Because I'm not happy if I don't have my coffee in the morning.
Altoids or chewing gum: Cottonmouth sucks, and these keep my helmet smelling minty-fresh. Which is a good thing, because my helmet has been through five summers in the desert and I'm pretty sure it's close to self-awareness.
Pen and paper: Presently a Pilot Precise V5 and a couple hip, black notebooks. I'm not picky about my paper, but I am picky about my pens. The ballpoint is my second choice. My favorites are the Varsity disposable fountain pens. I could write all day with those babies, and they never walk off. Anyway, keeping notes is good, and I can't stand typing into my...
Cell phone: My phone and I have an agreement. I don't like it, and it doesn't like me. That said, I do get a lot of use out of the weather application and the calculator. And I've used it as a flashlight in a pinch. It also does a pretty good job as an mp3 player.
Sunglasses: I do live in the desert, you know.
Tire pressure gauge: Since the ones gas stations will lend you never work anyway...
So, that is my current daily survival kit. It works pretty well for me.