The kids and I had great fun making our mousekeeping envelopes, and kind of used it as a "trip countdown". We get paid every two weeks, so we figured out how many nights we would be staying then counted back that number of paydays.
Each payday, we would go to the mouseforless site and the kids would pick out an envelope design. We printed it out, folded it up, and stuck a $5 bill in it, then sealed it closed with a Disney sticker. Finally, we put the finished envelope into our Passporter. By the time it was time to go, each day's pocket in the Passporter had a tip envelope in it, all ready to go.
Each morning, before we left the room, we set the tip out on the table; the envelopes are addressed "To Mousekeeping" and we would sign them from our family.