When we went to Yellowstone we were on a cross country camping adventure from MA to CA and back. Because of the restrictions on tent camping with the bears we did elect to stay in the cabins in Yellowstone but we definitely had food in our van the whole time and never had a single problem. We've also stayed other areas that have bears (in NH we had a bear sniffing the side of our tent) and again never had a problem with the food in the car. Just make sure to throw away wrappers in the bear safe trash cans when you are done and to make sure that you clear away crumbs.