Isnt that sort of an open ended question? I dont carry the same thing everytime I go out to take pictures.
With a closet full of camera equipment and a few bags to fit each shoot, this post could go on for every.....LOL
I never leave home without
1. Canon 1D
2. Canon 28-300 USM IS
3. Sigma 15 Fish-Eye 2.8
4. 2 Back-up Batteries
5. 2 Gig card in teh camera and one in the bag as a back up
6. Hurricane Blower
7. Microfiber cloth
8. A few freezer ziplock bags just incase the weather gets nasty
9. Canon 480 Flash with an extra set of batteries
10. Business Cards
Thats the bare minimum kit and the list could grow from there to the pick-up truck bed full depending on the type of shoot or occassion. I always leave the tripod in the car, as It's of no use in the house, so why carry it back and forth each time I leave?