The best investment I have made is a 2kw inverter for my car, since I've had the car we've only used it once (One powercut in 3 years is reasonably normal in the UK). The council was cutting trees down locally and the power was supposed to be off for 2 hours, for whatever reason it was out for nearly 12 and it saved all of our frozen/refrigerated food.
Anyone with an EV, I highly recommend you get an inverter for your car, far cheaper than getting a car > home set up (I think only Chademo supports it anyway) and it'll save you eventually! Make sure you know under what conditions your car will keep your 12v topped up, though so you're not caught out!