I make wooden cups. I use water-based polyurethane out of a spray can to waterproof the interiors. I find it a lot easier to use than epoxy in almost every aspect.

For the exterior and for cutting boards, I use a hard wax oil I make from linseed oil and beeswax. It's easy to prepare and I usually provide a small cup of it to whomever I'm gifting the cutting board.

I reuse small, glass jelly jars with screw-on metal lids, about 1/2 a cup in size. You do need to leave a layer of water on top, though, because otherwise the top layer will polymerize and leave a rubbery layer you have to remove the next time you use it.