I cleaned my car out today and put an organizing bin in it. The bin holds:
-Ergo
-Jumper cables
-First aid kit
-Diaper change kit
-Kleenex
-Returns or other items necessary for returns
-Spare blanket (would have snowpants, etc. in dead of winter)

We bring the diaper bag any time we take DD anywhere other than daycare.

What do you keep your car stocked with? Any suggestions for good snacks that withstand extreme temperatures?