I'd use a wipe-on varnish like Formby's or Minwax tung oil finish in low gloss. (Yes I know they might not really contain any tung oil) It'll will darken the wood a little but will make the grain show beautifully. For something as low-use as a keepsake box, you can get by with a couple of coats and you still have time for that. Good Job by the way. I love the elegant simplicity.
“We should be careful to get out of an experience only the wisdom that is in it and stop there lest we be like the cat that sits down on a hot stove lid. She will never sit down on a hot stove lid again and that is well but also she will never sit down on a cold one anymore.” - Mark Twain