My vv3 and MVP 2 never leave my side.
Serves both purposes: backup & provides for variety.
And if I'm heading out for much more than a quick trip to the lumber yard, I'll typically grab a a couple of extra
tanks - each one sporting a different flavor. More backups & more variety.
Because I PIF'ed my original ego type batts, I'm feeling the need to expand my backup reserves, so I've set sights on another of each vv & MVP.
And of course I have chargers in the car, and two of those handy dandy power-pack devices too.