I would wish I had just one more week to work on the piece before I played it that last time. Just one more week! Maybe if I had worked harder, been more serious, etc., I could have had it ready by then....
Probably the Raindrop Prelude. I like it and would be able to pull it out and play if decently and really get into it without much practice.
Of course.... knowing I would die the next day, I would take out a loan (to be paid off in two days

) and hire an assistant to help me track down the best possible piano to perform that piece on. And, what the heck, I'd just sit there and keep playing until tomorrow came along, being careful to keel over onto the keys so I'd still be playing something, even in death. And what if it ended up being a digital piano and I keeled over on the keys and hit some synth sound and that kept playing as long as those keys were still pressed down?

Yeah, and I bet there'd be someone in the audience who would sit there and wait and wait and wait and wonder when this 20th century piece was going to be over, but would be stubborn enough to sit there for a very long time, just waiting for the last simultaneity to finish.... (wonders if I should get a copyright on this idea since I've never heard of anyone playing a piece and ending it like that, even Cage.... someone must have thought of this before...) I could put up a little sign that says "I'm not finished with this piece until the sound stops." Wouldn't it be nice not having to worry about finding a parking spot that last time too? I'd park right out in front. And when you're really done, you might even have a chance to ask the composer, "Was that what you had in mind?"