I want to purchase a package of Egg Replacer. How long does it last and how should it be stored?

If you are talking about eggbeaters or something like that it needs yo be refrigerated. The expiration date will be printed on the carton.

The products I am familiar with have some starches and some leavening. The starches probably last years, but the leavening may lose its power. Check for 'use by'/'best by' dates. Store in that legendary 'cool dry place' -- you could transfer to a glass jar or put the box in a heavy ziplock bag with the air pressed out before sealing. Don't refrigerate -- it's moist in there.