Take your bag of marshmallows and toss them straight into a freezer bag.
Press all the air out of the bag, without smushing the marshmallows. Then, zip it closed.
Write the date on the outside of the bag.
Toss the bag into the freezer, but make sure it is not being crushed by anything.
Notes
Fresh only: marshmallows can get stale and once they are stale, they will not have a great texture when frozen and defrosted. So, make sure to freeze them when they are as fresh as possible.Won't be hard: due to the gelatin, the marshmallows won't be frozen solid. Just keep this in mind.Don't smash them: make sure you don't crush or smash the marshmallows in the freezer or they will become more compact and hard upon defrosting.