Envelopes Homemade RattyRat's Review: Envelopes can make great treat dispensers. Just throw a couple treats into any sized envelope, and seal it up. Make sure that it is the lick and seal kind, not the peal and seal kind. Our rats have lots of fun dragging theirs off, and then chewing through it to get to the tasty surprise inside. It's like giving them a little gift to open.