I have just recently starting getting more serious with cycling. Mostly 12-25 mile recreational/fitness rides. I also have had my first away-from-civilization flats and have come to respect being prepared with a good seat bag kit. But I also want to travel light, and don't like a large dumpster bouncing behind my seat. So I have been trying to figure a small kit for my seat bag with just the essentials yet still keeps me somewhat prepared:

1 tube (considering omitting, thoughts?)
CO2 inflation system (only one cartridge)
Patch cement and "scrubber", 2 patches, wrapped in a rubber bad
Crank Bros Multi 17 (going to go smaller here soon)
cell phone
$20 bill
2 keys, house and car, attached to above tool

Considering adding:
A dozen Ibuprofen tabs
1 gel for emergency calories

Please offer any tips on mine (remember, for my needs) and share yours (whatever your riding needs).