10-15 years ago GNP was easy to find a campsite, 3 years ago when I went we got there early before noon and the web site and sign out front said full we were able to get one site. For YSNP there are always the NFS CG's in west yellow stone to stay in like Bakers Hole CG and that is easier to find a site. If you stay off site go into the park in late afternoon and drive the wild life loop in the northern part of the park you have a greater chance of seeing animals late afternoon until dusk. We saw about 2 grizzlies and 4 black bears one was a cinnamon black bear at that time. Both parks have good fishing caught a huge cutthroat trout in Yellow stone lake and many smaller ones in GNP along with a 22 in lake trout in a stream also. No fishing licence is required in GNP.