I just got finished with my coupon books! The coupons ended up being different sizes so I also couldn't figure out a good way to assemble them.
I ended up punching a whole in the upper left corner and attaching the coupons to a ring. (Like a key ring with a clip) I then tied Disney themed ribbon to the ring. It turned out cute and the kids can easily clip it to the stroller or backpack.
Now I just need to decide how to use the coupons! Have the kids give them to me when used or have me initial them with the date and time??