And get the passport card, too!
While it does not suffice as a passport, it sure makes getting a replacement easier if something happens and you need to verify your citizenship and identity.
Ed
The passport card does (or used to) suffice for both Canada and Mexico. My wife decided she wasn't going anywhere but those two countries so just opted for the card. I got the passport, which I used for So. Africa. I'm going to have to renew in the next couple of years again.