As a non US citizen the discount pickins are slim. You can get the National Parks entrance fee card, buy individual state annual passes which vary as to what you get & get the Passport America & Good Sam memberships. You can also get the various discount cards at grocery store chains & truck stop chains.
Have fun. We bought ours thinking that 3 years would satisfy that travel itch. That was in 2007. We are still at it over 150,000 miles & 1500 nights on the road later.
The US & Canada are huge places to see. Take the time to soak it all up.