A definitive answer requires knowing precisely how many watts (thus how many amps) things draw, both on startup (surge) and for running. This information should be posted on a plate, tag, or sticker somewhere on the device.
You then must add up both surge wattage and separately running wattage, and pick a generator capable of handling both. Things that have a motor, the AC for example, will require 2 to 3 times the running amperage for startup surge. Things without a motor, the fridge for example, will draw the same power on startup as running.
It is possible to get an AC that can handle only the AC, but not the AC and the microwave at the same time. Using it would thus mean don't attempt to run both, or you will knock the generator offline. Typically (but not always) this requires shutting it off and restarting it, but it might mean resetting a circuit breaker.
Without knowing how much power that AC uses, one can only guess at the most appropriate size generator. Otherwise, you could buy the biggest one possible -- which will, of course, cost a lot more and burn a lot more fuel.
Colliehauler is right, theft of the generator is a major risk.
