BRUSHES! They are MAC's must buy!
The fluidline eyeliner is awesome, and the liquidlast is realy good if you're gonna be really active that day. You know, swimming, sweating, stuff like that.
Beware: it WILL NOT come off easily! Use an oil based remover to take it off. Because all your scrubbing with soap and water will be in vain.
The foundation... *sigh* only use if you have really nice skin. Otherwise it will look cakey, fake, and it'll clog your pores big time! Sadly I have dry skin so I can't wear it.
If you do get the brushes don't let them talk you into the brush cleaner. It's really harsh, makes the brushes shed and lose their shape. Baby shampoo or hand soap is best for cleaning the brushes.
The people are really nice and if you mention that it's your birthday they'll be even nicer and match everything to your skin tone, preference, etc.