We got another large box in the mail (something we get twice a month) and this one became a felt Christmas tree! Katie can decorate and redecorate the tree over and over again.
We cut out a Christmas tree shape from the cardboard box, reinforced it, covered it with green felt and glued it together. Then we spent about 20 minutes making Christmas lightbulbs, glittery balls and fun ornaments from felt.
I sewed together a "gift" looking envelope to put all the ornaments in when not in use.