With LEDs the batteries will last virtually forever but are best for task lighting as they are very directional. I made myself an LED headlamp using 5 white LEDs and 3 small 6V camera batteries. I've used it nightly for over four years while feeding the pony and the batteries are still operational.

Propane lamps as Sorcha described are still the best way to go for larger area flood lighting. We've never screwed our lights to anything more than a 1 litre bottle. Two 1litre bottles of propane would be more than enough to last the weekend no matter how late you plan to party. ( You'll probably be able to save the extra bottle for for next year or the next time you have a power outage).