I like to take premade palettes and compacts, so that I'm not hauling around my palettes I've put together myself. Two lipsticks, one or two lipglosses, one premade eyeshadow palette, eyeshadow base, one cheek highlight, one contour colour, one blush, mascara, black eyeliner, pressed powder, concealer, foundation, brushes.
When I wasn't going to be home for Christmas, I packed my warm eyes palette from this year because it gave me a number of pretty options in secure packaging, my Ungaro beauty powder (it works as a blush for me), a red lipstick, a nude lipstick, a dazzleglass, a pink-nude gloss, and the rest of the things mentioned above.
For me, it's about maximizing options and be ready for anything while not hauling along a ton of stuff.