What are good apps for use on tablets when traveling?

Weather Underground & Accuweather---sometimes one of them won't work and the other one will

GasBuddy

Waze--for traffic--gives you real-time updates

Google Maps

I agree with looking at a map beforehand. But I also check traffic any time I make a rest stop, or before hitting a congested area, to see if an alternate route would be helpful. Has saved me a lot of time and frustration.