I’m sure you’ve already used this by now, but polyurethane or lacquer should be good enough to seal it. I would do a few coats of either. You just need a good bit of lead time. Most of those things are “foodsafe” once “fully cured,” but depending on what it is, that could be weeks to “fully cure.”
Yeah, I cut the walnut, then the glitter paper, then glued!
BTW - as you can see, the glitter cutout is smaller than the walnut. This isn’t as simple as scaling down the original text. Instead, the walnut design has an outline, which gives it extra thickness. For the glitter design, I removed the outline to make it a “thinner” version, so that some of the walnut is exposed when the glitter cut out was placed on top. Hope that makes sense!