If you're already saving your fail prints, you're doing awesome! If not, you should start saving them! You have the option to store them how ever you find efficient and convenient. Keep them in garbage bags or plastic bins. Over time you may find yourself with lots of junk, but you should hang on to the big stuff. You may discard the stringy stuff.
If you're interested in producing consistent colored material, you'll need to separate your parts. You should be able to distinguish ABS from PLA and sort accordingly. You can use whatever method of sorting, but we used a few shoe dividers to keep the parts separated.