Fun Doesn't Have to be Expensive, Just Creative

Never one to excel at playtime, I'm finally learning that it isn't as hard as Fisher-Price makes would like me to believe.  Three years of purchasing random trash from the toy stores has lead me to this... a stack of toys that actually entertain Tiny & the Tot:

Clockwise from the top: 

1. A nap spot for "Monster"/rocket ship/pirate ship/cage for Tiny (though she doesn't enjoy that as much as the Tot)/indoor canvas for sidewalk chalk, 
2. "Suuuuuuper Neena's" cape (Thank you WonderPets),
3. a Red straw from Sonic ~ the most highly prized, most often sought-after, most frequently fought-over toy on the planet, 
4. Tiny's crinkle wrapper (note, this is a one day use toy, but the Tot usually has a new one for her after her first nap), and 
5. last but not least, a drum/pony caddy/circle template/tea party plate/scooper/shaker/hat.

I used to dread inside-days, but a bit of creativity goes a long way, and my littles seem to be full of creativity.  What ideas do you have for inexpensive/free indoor activities?  Brainstorming together, I bet we can come up with a winter's worth of fun. ~ It's Plain and Simple As That.