update:
Well I experimented with these yesterday and froze a few overnight. They are delicious!
Just halve & pit them and as Christie stated get as much air out of the bag as possible. I am not sure how long they will last, but I am sure you can get a bit out of them...The taste nice and slushy/icy, already Ashley approved
BTW, you can also freeze grapes for a nice, slushy treat for your kids!