What can I do with egg whites

If you don't mind trendy, try cloud eggs:

http://www.independent.co.uk/life-style/food-and-drink/instagram-breakfast-craze-how-to-make-cloud-eggs-a7723776.html

Here's a handy link to some earlier hotline threads on this very topic:
https://food52.com/hotline/search?q=egg+whites

Pavlova! Meringues! Swiss Buttercream! Coat chicken for breaded chicken cutlets. Freaze them. Use in shaken cocktails for foam and body.