Amazon has The First Years On-The-Go Booster Seat $13.40 (Reg $20.99). On-The-Go Booster Seat seems to appear and disappear like magic.
Pull out the valve and it self-inflates into a sturdy and comfortable full-size booster seat. Then press out the air and fold down the back once mealtime is over. With a self-carry handle, it’s compact, lightweight, and has an adjustable safety belt with T-restraint to help hold your child securely. This is definitely one for your mommy bag of tricks!