What to do with leftover crumb topping?
If you really don't want to bake anything else, you could bake the crumb on it's own. I'd be sure to put it on parchment or a silpat to avoid it sticking to the surface below. Bake it at 350F or so until it's browned. Once it's baked, it should last a while as long as it's stored in an airtight container. It would probably be good as an ice cream topping?