Just a suggestion for an activity DD created on her own.
One day, I was cleaning out the car and took my yoga mat inside. She was rolling it up, down, jumping on it, doing flips, etc. We turned it into a sticker mat, we wrote on it with chalk, we pretended it was a dress or she was a burrito, etc. Then I pulled out her old daycare nap mat and put her stuffed Loch Ness Nessie in the middle. We played a jumping game from mat to mat so that Nessie didn't nibble her toes.
She had the MOST FUN EVER. With a $10 yoga mat. Highly recommend as a "new toy" for your arsenal on rainy days.