While traveling cross-country with my new wife, we quickly discovered that van camping wasn't so easy as just finding someplace on the side of the road and parking. Through trial and error, we discovered three apps in particular that helped us on our journey.
GasBuddy
First and foremost, I need to clarify. I only recommend this app for use during the roadtrip; do NOT leave this installed on your phone. (More on that here) While we had the paid subscription for this app, I would recommend simply using the free version of the app. Simply put, it allows you to compare gas prices at local gas stations. Additionally, you can search for the gas prices at your upcoming locations; we found it useful for figuring out what gas prices would be like in the towns we were spending the night at. We would fill up each morning before heading out, and it as worthwhile to save a few extra dollars each day.
Sekr