Step 1: Reuse.
If have animals that like to hide use cereal boxes or shoe boxes and cut holes in them. This is a nice way to save money because the hide boxes are about $15-20.
Step 2: Be creative.
Step 3: Ideas.
A box to make a house or play pen for your hamster.
A can to make a trap for your loose rat.
Wood chunks into gnawing blocks for you're rabbit.
An old coat hanger into a hanger for those wood blocks.
Not showed I made a box into a house for Rocky.