A seat post that seizes inside the frame is one of the most annoying repairs out there — and one of the easiest to prevent. Once or twice a year, pull the seat post out, wipe it clean, and put a thin coat of grease (or carbon paste for carbon posts) on it before sliding it back in and setting your height. This stops corrosion and rust from locking it in place, especially after our salty Canadian winters.
Five minutes of grease today saves you a stuck-post headache tomorrow.