What is the minimum I need to keep in my saddle bag?

[Zen]

Two tubes, tire levers, multipurpose tools,money, I.D, copies of insurance cards and emergency contact,cell phone and I can't go anywhere without my camera...old photographers never retire.

You could probably do without the camera but you never know what kind of interesting road kill you'll see.

[bmccasland]

bag #1, under the saddle contains: tool kit, spare tube, CO2, tire patch kit (bike / tire repair stuff)
bag #2, "Bento Box" on the top tube contains: ID, insurance card, benadryl, albuteral inhalor, cell phone, car key, and sometimes a Clif bar.

[anakiwa]

Tube, patch kit, tire levers, hex-key/screwdriver tool, and $20 bill (this item gets used most often). I have a pump on the bike as well. I have a bag on every bike I own (it's worth it not to have to worry that I'll have forgotten it when I most need it).

Cell phone depends on where I'm riding (there are a lot of places around here where a cell phone is just dead weight).