You can get by without carrying a full tool set in your trunk, but don't underestimate the value of a portable power bank. Whether it's a small one with a pair of 110-volt outlets to charge your phone in an emergency or a honking unit with every type of plug-in and more output than the sun, they come in handy. If you already have one, good. If you don't, these Jackery deals on Amazon are worth looking into.
Spend as much or as little as you want, but just know there's probably an exact model to fit your actual needs. I don't have to have a full-on generator that'll run an industrial complex, but you might. That's the beauty of it all.