If you're going to use the extra grains soon (ie; in the next month), the cabinet is probably OK. You can always stick them in the fridge or freezer, too. They will keep fine.
As for the extract: Yes, save it. You can always toss it in another batch later OR use it instead of dextrose for priming at bottling time.
If it's liquid, think of it like you do maple syrup. It will last quite a while, expecially in the fridge. If it's dry, it will keep for a very long time cold or room temp.
I'd put everything in ziplocks and put it in the fridge. It'll still be good when you brew the next batch.