The ones I have right now are:
GasBuddy - for gas/diesel prices
GoodRX - for when insurance won't pay and/or the discount may be bigger than what you get thru insurance
Pandora - for different music stations, free if you are ok with some ads every now and then
Audible - for books to listen to while driving
The Weather Channel - for weather on the go
CoachNet and Progressive - claims and help information at your fingertips
Base Directory, AllStays CRV Military, UC Military - all in helps of finding bases with FamCamps
Rest Stops - Locates rest areas along your route with how far they are
Hotels.com and Agoda - used both for hotels while traveling both in the US and the UK
My Credit Union apps - which ever bank/credit union you have I would access their apps to keep an eye on accounts while on the road fast