I carry a fair amount of stuff in my boat and on my person whenever I kayak.
In or on my pfd, I have a knife, folding saw, a tiny drybox with a led headlamp and a lighter, two mini pulley thingies, 2 locking carabiners, two prussicks, a glow stick, a compass, and a whistle. I also carry a sling of webbing around my waist with a locking carabiner and a paddle carabiner. This is how I hit the water, whether its raft guiding, steep creeking, or taking my son out in a ducky. I used to carry a bag valve mask, but decided I'm more likely to hike out in the dark than perform cpr, so i swapped in the headlamp and lighter so I have something even if I lose my boat. I used to depend on the glowstick, and still keep one in there, but it's hard to hike through rhododendron with just a glow. Trust me. As for the lighter, well, I think Jack London painted a pretty good picture.
In my boat I always carry a 70' spectra throwbag, and an emergency kit packed in a nalgene bottle. My kit contains a large trashbag, lighter and rubber for a fire, sam splint, ibuprofen, maxi pad and a few band-aids, space blanket, duct tape and a paddle carabiner. The nalgene bottle can be emptied out and used for water, with the other gear put inside a ziploc from the kit. The trash bag can be used as a splint, to carry water, groundcloth, poncho, partial bivy sack, and covering a large wound. The sam splint is a luxury, but it makes splinting so easy I bring it. I'm pretty light on first aid equipment, but for simple day trips, your priorities are going to be stabilization and evac, not particularly treatment. Maxi pad for blood, band aids and duct tape for stubborn bleeders, ibuprofen for pain and inflammation. I've taken an EMT class, and followed it up with a Wilderness EMT upgrade, so I feel comfortable with my level of knowledge. If I'm going in somewhere more remote, like otter creek or red creek in the winter, I'll throw in a dry bag with some gloves, an extra fleece, and a warm hat.
Comments? What do you carry?