What alternate ways are there to get into a garage when you don't have the opener?
Typically, garage openers have a release pull that hangs down from the track.  When closed, this release will be close enough to the door to get if you drill a 5/8 inch hole about a foot under the where the opener attaches to the door.  Fish for the line with a wire coat hanger and then pull to release.  It will take a couple of tries but you should be able to do it.

Once open, go to your hardware store and get a garage door quick release lock and install it into the hole you just drilled.  In the future if you have a power outage or a failed garage door opener you will be able to get back in.