My husband is a big fan of grapes. And although I like them, we just don't make it though a whole container before they go bad. My husband also loves frozen grapes. So when I find fresh grapes on sale, I buy them up! I will leave some out for him to eat fresh, the rest I freeze.
Pull all the grapes off the vines and place in a colander. Rinse well with cold water and then allow to dry, either in the colander or pour them out (carefully) onto a clean towel. Once dry, spread them out on a cookie sheet, they can me in more than one layer. Place on a level surface in your freezer for 12-24 hours. Try not to accidental dump them in the freezer. There are still a handful of grapes laying in the bottom of my deep freezer right now. :o) Once frozen, store them in a zip top bag.
My husband will get these out when he gets a sweet tooth instead of hitting the cookies or ice cream. They also work great in smoothies as a substitution for the ice.
This saves you money in two ways. You can actually buy frozen grapes, but they are usually more expensive than fresh. And it saves you from throwing away good grapes because you didn't get them all eaten before going bad.