Wow, the variety of answers here is mind-boggling. Even though they are all essentially the same answer, they all take different routes to get there! Easy answers for "most" RVs are as follows:
Fridge uses either propane or 120VAC, but always needs 12vdc for the control board.
Water Heater uses propane (some can also use 120VAC), but also needs 12vdc for control board.
Furnace uses propane for burner, and 12vdc for blower and control board/thermostat.
Air Conditioner uses 120VAC, but also needs 12vdc for control board/thermostat.
Stove/oven uses propane only.
Microwave uses 120VAC only.
Water pump uses 12vdc only.
Lighting uses 12vdc only.
