If you're disassembling something where you need to keep track of the pieces to put it back together, set it in a pizza box as you work, the raised sides of the box will keep everything right where you need it.
Along those same lines keep craft projects in a pizza box as you work, it will catch spills, glue, glitter - you name it, and it will give you a spot to put tools down as you work.
A clean pizza box makes a handy lap desk for kids in the car, they can have their supplies handy and don't have to worry about crayons and markers rolling all over.
Line a pizza box with foil and you can use it to transport cookies or other treats when you don't want to forget a container somewhere. Like a picnic or school event.
If you're hard up for inexpensive artwork, wrap a pizza box in some pretty paper and hang it on the wall.
Just a few ways to recycle some old pizza boxes, I'm Mrs. Fixit and it's just that simple.