I love using the coroplast in the bottoms of my bags. It's also what I wrap my fabric around to arrange my stash.
The best part of using it in bags is it tolerates water, so if the bag accidently gets wet, the bottom doesn't fall apart. It also is a good foundation if you like to add "feet" to the bag.
I used this to make temporary gates in my house for puppy training too, but that's another story.