I always keep a gallon-sized ziplock in my freezer, filling it with roots, stems, tops, peelings, and stragglers as I cook. Wilted or dried-up bits are fair game, but don’t include anything that has already started to spoil or rot. Things from the carrot family and garlic/onion family make particularly tasty broths. To make chicken broth, I’ll save the bones from a roasted chicken or two and add them to the vegetable scraps.
When the ziplock is full (you’ll find this doesn’t take long with a CSA share), I simply dump the contents into my crock-pot, fill it with water and a sprinkle of salt, and set it to low while I go to work or bed. When I return, the scraps and water have transformed themselves into a rich broth. The same could be done in a large pot set to simmer, but don’t leave it unattended like you would a crock pot. Separate the broth from solids with a fine mesh strainer. Freeze broth in clearly labeled containers and store for up to 6 months.