You may have to call several to find one who can get to you within any reasonable amount of time. A book or magazine to read if you get stuck in your car. Small first aid kit. Large Zip-Lock bag to put wallet in if you have to wade in water. Extra pair of socks.
Dry feet are a blessing.
It is easy to store quarters in the glove box inside one of those plastic film canisters from a roll of 35mm film. Cut a hole in the end and you have a poncho. Use it as is to keep stuff relatively dry if you have to leave your car. If you have to be rescued at night this could come in handy. Camping supply departments sell cheap ones.