DIN to Yoke
Yoke to DIN
copy of cert card
copy of DAN card
copy of drivers license
Yoke O rings
DIN O rings
four 5 dollar bills
tiny spare pair of reading glasses
defogger
plastic tie wraps (small and large)
cylume light stick
BIC cigarette lighter
small pocketknife
Allen wrenches for DIN adapters and regs.
I also carry a Leatherman with me as well.
Other than the Leatherman and the Yoke to DIN, I keep all the above in a small plastic waterproof Pelican case. I think a few bandaids in there would not hurt as well.
I was going to add a spare mouthpiece, as I kept biting through mine, but I ended up getting one of the moldable ones, and its impossible to bite through (so far) seems like its going to last forever. I dont like carrying a bunch of useless clutter. When I carried mask and fin straps and hoses, and all that other stuff, I found I rarely needed them, and I couldn't see the forest for the trees, and many times did not have the things I REALLY needed to save the dive. You can eliminate the need for a lot the dive saver things by making your equipment rugged. For instance, I switched out my fin straps for spring straps, switched my mask strap for a slap strap, and once over test my gear before I leave the house.