My next one will have 50amp service, outlets everywhere inside and out, even inside the lower cabinets for hot water tank and pump hook ups. Minimum 50 freash water supply, outside lighting so I can see all arounf it at night, on board Honda power inverter generator.
You will definaltly want ac and heat if you live in the climates to use them. There is more but this is what I can think of right off hand. Give extremebbqtrailer.com a call they are here on the brethren somewhere and make some nice trailers from what I have seen.