personally, i don't like to practice my pieces the day i'm performing them, maybe not even the day before, cos anything i do just before that is a mistake, i'll do it in the performance, eg. i was practicing before an exam at school, and my friend walked in on my playing and i messed that little bit up, and then in the performance i messed it up too.
some people may disagree with me, but i like to warm up with my good ol scales and hanon, just so my hands are moving and won't be stiff at all. if you're going to play any pieces at all, then choose ones you won't be playing for the performance, studies would be good i guess.
but if you're anything like me i'd recommend not practicing your pieces beforehand