I use plastic quart ziploc bags and freeze my slices. I place 2 slices in each qt. bag...sometimes a tight squeeze, but do-able...and then place them back into the original plastic bread bag--i.e. double sealing. When you need the slice(s), take out and let thaw for a few minutes in the ziploc bag. Your slices will be like new. [The slices aren't as nice if you microwave them.]
We are currently working on a special loaf of Italian bread that we got last October while on vacation; the slices are still good. Good luck!