Buy marshmallows on sale and freeze freeze them in bags until you are ready to use them. They defrost and work quite nicely in recipes and keep longer.
Substituting Marshmallows and...
Substitute for Marshmallows?
Freezing Baking Soda and Baking Powder?
Marshmallow Crisped Rice Treats (Giant Roasters)
Making Homemade Marshmallows
Freezing Seafood Dips and Spreads?