Be sure to pay attention to the cancellation period for things like the Poly Luau.
We tried to cancel our ADR the day before, but they wouldn't let us because they had a 48-hour cancellation policy. (This was even more frustrating because our ADR was scheduled for the day after a hurricane blew through -- we thought it might be cold and rainy for our ADR, so tried to cancel, but were told "NO!" WDW is not flexible on things like this.)