You can also get a pretty big inverter and attach it directly to the battery. A typical alternator can provide about 100 amps, or 1200 watts. In theory the battery could support higher draws for short amounts of time as well if the alternator can't keep up for a small surge (like a fridge running a cycle). Probably not nearly as efficient as an actual generator, but for occasional one-off usage it works in a pinch.

My EV doesn't support bidirectional stuff like that, but I've got a quick connector on the battery for that purpose. Same concept, but it's the DC-DC converter doing the work instead of the alternator. Worked great, but of course the power came back on 15 minutes later