Your cake recipe asked for more egg yolks than whites, or vice versa, so you are left with 2 or three yolks, or whites, and you don’t know what to do with them. Don’t throw them away.
Place the yolks in a plastic container, add enough cold water to cover them, and keep them covered in the fridge for two days. If you want to keep them longer you can freeze them. However, as the yolks thicken or gel when frozen you must beat in the yolks 1/8 teaspoon of salt or 1 ½ teaspoons of sugar per ¼ cup of egg yolks, that is about 4 egg yolks. Label the container with the number of yolks and date, and don’t forget to mention whether you have used salt or sugar. You can freeze them for a maximum of four months. You can use 1 tablespoonful of thawed yolks for 1 large fresh yolk.
Egg whites can be kept in the fridge in a container for about a week. You can use them to make meringues or omelets. If however you want to keep them for a longer period of time, you can freeze them. Place them in a freezer container and seal tightly. Again, don’t forget to label the container with the number of whites and the date. You can use 2 tablespoonfuls of thawed egg whites for 1 large egg.
Freeze eggs in small quantities, so that you don’t defrost more than you need. It is not a bad idea to put them in ice cube trays and when frozen you can transfer them to a freezer container and label accordingly.