If these are nice things you expect people to hang on to for years, then you could go for something like Rustins Plastic Coating, and know that they'll be bomb-proof for virtually ever. If they're a throw-away item intended as a stocking filler, then whatever varnish you've got lying around. They'll last a few months.
Something like the Rustin's product would be extremely durable and hard wearing. Sorry to disagree with Mike on the second part of his post though, if you use any half-decent polyurethane you could get far more than just a few months out of them! Do it right and they'll last years, maybe more than a decade. How often does a varnished table or kitchen counter need refinishing?
You don't gain the full protection varnish is capable of if you apply it too thinly, something that is increasingly common these days (even commercially). So when I say do it right I mean build up a sufficient thickness, e.g. three or four full-strength coats, or the equivalent if you apply it like wiping varnish.
Plenty of time till Christmas so this shouldn't be an issue but it's also important to let varnish cure fully before it is put into service. Not doing so is another cause of early failure.