Here are some things we've done:
Get out blankets or sheets and build a fort (if you have an extra table or card table that's a great base!) Toss in a flashlight for extra fun.
Fill the kitchen sink with bubbles, arm your kiddo with measuring cups, spoons, strainers, etc.
Pour dry beans in a big bowl with spoons and measuring cups. It's like a mini-sandbox.
Get him to help you with some of your tasks. My little boy loves to help me carry dirty laundry and toss it into the washer! (even if it's just a t-shirt)
He loves to use the swiffer... he might just be moving the dirt around, but some of it sticks!
Make paper airplanes.
Put photos in a little photo book (they don't have to be cropped or decorated) and let him look at them. He'll probably be excited to see all the people who love him and the places he knows and will tell you all about what he's seeing!
Use toys in odd new surroundings. Play with the bath toys in the livingroom. Take the toy dinosaurs into the bath. It makes them new again.
Clean out some space in the garage (or back the car out) and let him ride his trike in the open space.
Rotate toys - one night, after he's asleep - sort thru his toys and remove 1/2 of them! After a few weeks, swap the toys! He'll act like they're all brand-new again!! (really)
Free outing... the indoor playroom at Cedar Ridge Christian Church in Lenexa. There's a coffee shop attached, so you could buy a drink. But it's free. Free entry, free Wi-Fi. Very cool. Often busy, and kinda loud - but free and lots of fun for your little one. Great way to beat cabin fever!
Hope those ideas help you!
T.