Egg whites freeze well. Put them into a custard cup, and keep a tally of how
many are there on the side of the cup using a grease pencil or pen on
masking tape. When you have enough for a full recipe, say, or meringues, you
can thaw them and use them. Just be sure to keep them scrupulously free of
any oil or fat, as that will prevent them from whipping up (if you want to
use them whipped, that is).