You've probably discovered just how easy it is to do. Look on-line for a "Refrigerator Pickled Beets" recipe. Of course you need vinegar and sugar, and the basic spices are cloves and cinnamon. Add in some white onion slices. Some recipes call for allspice. Mine uses a couple bay leaves and a handful of peppercorns. I make them in the morning and they're ready to eat by dinnertime.

Bonus: you can drop a few hard boiled eggs in with the beets.