A socket passthrough that reads out watts and accumulated watt-hours. Under ten pounds, and it settles arguments that otherwise get settled by guessing.
It is on this list because of a specific problem. Power for cooking turns on knowing what an appliance really draws, and the advertised figure is often not that number. A microwave sold as “800 W” is quoting cooking output, not consumption. An electric grill draws near its rating continuously while a hob cycles. A kettle is worse than both and briefer than either.
Plug the thing into a mains socket at home, cook something on it, and read the watt-hours. That is the number to size a battery against, and it is measured rather than inferred.
Doing this before you buy a power station is the cheapest possible way to avoid buying the wrong one. Doing it afterwards is how you find out why the hob keeps tripping it.