I've got a couple of 12V LED strips that were originally powered with wall warts that I use on battery power. I also have a few 12V CFLs that work well too. I get 'em at Menards but Home Depot and many RV/camping/boating stores and even some truck stops have them too.
Another option would be a 12V LED 'puck' lights. Most of them I've seen at the big box stores are powered with 12V wall warts.--