Trying a few things from this Plant You Scrappy Cooking book... I've kept green onions alive in water before, but now I'm trying growing carrot tops and celery bases.
I also set a bunch of carrot and celery sticks in jars of water in the fridge for easier snacking. My grandmother would be so proud. She used to set carrot and celery sticks out on the table at her farm when we visited. As a kid I was grumpy about that, but I've since come around.