The key is to mix and match all your clothes so you can get more than one outfit from each. I also wear the same outfit for both formal nights.
Stick to one basic color scheme (black, white, khaki) and make sure all tops and bottoms cross match. I take 3 pair of shorts, 2 slacks, 5 tops, 1 pair of black slacks with top (formal). If needed, I use the laundry service.
I also only pack 2 pair of shoes/sandals.