Off batteries... If you have at least 200 amp hours at the c/20 rate (IE a pair of Group 29, DEEP CYCLE, 31 DEEP CYCLE (Not Marine/Deep cycle in both cases) or a pair of Golf Car batteries and an inverter at least 1500 watts (mine is 2000) you can run a Microwave for a short time, the more battery the more time (i have over 500 amp hours).
Off "Shore" power.. 20 amps one big ticket item (Microwave, Water heater, Air conditioner) Provided the batteies are not sucking major re-charge amps of your converter..
Off 30 amps. 2 of the above
And if your trailer is wired for 50 and you have 50. All you can eat.