Be careful using pallets, especially if you don't know what they where used to carry.
On the way to the campground, keep you eyes open for the firewood stands on the side of the road. As long as they are near the campground, you are fine burning that wood. Also, it is usually less per bundle, and much larger bundles, than at the campground store. Depending on what kind of camper you are driving, you may want to get setup at the campground and then go back for the firewood.
Easiest thing to do, if you are only going to have an evening fire, is to buy the $5 bundles from the camp store. Of course, it usually takes at least two bundles for a few hours fire.