During the extent of our month of rain (plus my 2 week virus), I was forced to recall any and all things I have seen or heard of doing indoors with children in order to keep up with my toddler's activity demands. I vaguely remembered seeing a juice box sail boat featured in a Parents magazine once, and with some help from my main man Google (why would anyone use any other search engine???), I happened upon the very magazine image I was looking for!
Here's some photos of the how-to via Inchamark:
Freida really enjoyed the process of watching something as simple as her apple juice box + a piece of scribbled paper turn into a sail boat (and I felt good knowing this type of "play" was great for her cognitive advancement of understanding cause and effect). Plus, setting the boats adrift was definitely a hit! It kept her busy for a nice little while (she even took them out to play with again after her nap - score!).
(I'd advise you not to use marker on the sails like I did - the ink bled all over as soon as the little boat tipped...)