I just bought more saddle bags and flat repair kits, so there is one for each bike. I figure it adds about $50 to the cost of having another bike, so I just factor that in when buying more bikes. Plus the kit can be customized for each bike. Touring bike gets a bigger bag and a minipump, club bike gets a teeny weeeny seat bag and co2, family bike gets all sorts of stuff.

But I think it would be very easy to assemble a "bike wallet" that has your mini-tool, co2, tube, id, credit card, and cash in one easy to grab rig. The only problem is that I would forget to grab the bike wallet, guaranteed. *sigh*