The are great for holidays and are perfectly suited for Passover, which comes up in mid-April because it is mostly egg whites and sugar and love. You can always add in extras. The ones above have crushed peppermint sticks sprinkled over before baking, but you can add chocolate chips, cocoa, flavorings... anything you fancy, just add them in after all the sugar has been added.
One word of advice though, since you are not using cream of tartar which stabilizes egg whites (because it is made of grape skins a.k.a yeast central) make these on a day with low humidity (rainy days and meringues don't mix) and make sure your mixing bowl is absolutely free of all grease, or the egg whites won't inflate.
3 egg whites (or about 1/3 cup pasteurized liquid egg white)
1 cup white sugar
1/2 teaspoon distilled white vinegar
1/2 teaspoon vanilla extract
1 pinch salt
Preheat oven to 300 degrees F (150 degrees C).
Line two large baking sheets with parchment paper.
Whip egg whites to soft peaks using an electric mixer.
Gradually add the sugar, vinegar and vanilla while whipping to stiff peaks.
Load meringue mixture into a large plastic storage bag (or piping bag) cut off the corner (a few cm only) and pipe rounds onto your parchment paper lined baking sheets. Leave about an inch between cookies.
Bake for 20 to 25 minutes in the preheated oven, until cookies are dry.
Crack open the oven door and allow to sit with the oven off for at least an hour.