HOw often to give surprises/treats

[disneymom3]

We will be driving down to WDW from MN in Dec. We plan to leave on a Friday evening. DH willl have slept all day and will drive that night and I will drive starting the next morning. We are hoping to make it to just south of Atlanta by Sat eve. Kids sleep well and do well overall in the car, but we've never gone this far. I have little gift bags and treats planned to be distraction etc. Some new coloring books, kids music CDs, stickers and that kind of thing. But I am wondering how often you would estimate you give things to your kids as you are driving along. Any ideas to help me estimate. The two who count are 6 and 2 and 1/2. The baby is not getting much new!

Thanks!