Certainly, you can get disconnect switches and wire them into generators. Or you can just pull the plug if we're talking a portable generator, or stop the generator.

The wiring itself should be properly provided with a circuit breaker to prevent it from starting fires. I understand that your heater and your cooking device may have their own issues (as they are supposed to get hot).

Am I missing something?

Be careful with that laptop. I would not plug it into circuits that I intended to "kill" as needed. Laptops do have an internal battery supply and that should protect it from a power fail shut down. However, PCs need to have an orderly shut down procedure to keep them in good health and I would not trust that the laptop could change power sources without a problem. The main hazard would be high voltage switching transients can appear in the power leads when interrupting large loads.

Eh? I've never owned a laptop that didn't handle having the AC power just fine. The first thing that happens (usually out on some device on the cord) is the AC is converted to DC.

I would not trust that the laptop could change power sources without a problem

They all do. This isn't a worry.