What do you take with you on the bike?

I train with: spare tube folded tight behind my seatpost, and a Bento TRZ that holds 2 levers, microflate with CO2 x2, glueless patches, Crank Bros multi17 tool, cellphone and a $20 bill. 

When I race, I leave the cellphone at home and throw in a couple gels, and all the rest stays. I mounted the Bento at the intersection of top tube and seat tube, reversed so that the leading side is the shorter, and the taller side is up against the seat tube. 

Bento TRZ: 

I carry (almost) exactly what Tom does, and in the same bag.   If I had a mini tool, I'd carry that as well.  Races, I just leave the bag on the seatpost, same contents

I do differ on the air chuck though. Bought one on a friend's advice and I found it hard to control.   A better (to me) and not much larger option  is to use one of these and leave off the screw on "cartridge carrier" for lack of a better word.  Much more control getting air in the tire.  When youonly have 2 cartridges and you're on the open road, really want to make sure you get it right

I also carry one more tube in my jersey if I am riding long or more than 2 hours alone.

THis type of inflator, not necessarily this one.  All I carry is the top part.  Note you have to use threaded cartridges (same as the air chuck)

http://www.coloradocyclist.com/product/item/INNPPU82

Pretty much I carry the same as everyone else is describing (spare, some cash, cell phone on training rides, patches, CO2).  But I also carry a combination frame pump-CO2 inflator.  Mine is a longer version than this one below.  I like the idea of having a frame pump in case I have complete disaster - e.g. three flats, so I am SOL since I only carry 2 CO2's, and my cell phone dies, and I would end up needing to use the frame pump. Or if I see someone who has a flat and I have already used my CO2.  I like the longer pump since it is easier to fill the tire, but since I added CO2, I haven't needed to use it, so I am thinking of upgrading to the smaller pump.