Port is usually a good thing to put down (I had one from my birth year on my 30th birthday).
Or choose a good red wine, however you wouldn't know if this is a good year (vintage) until the wine is bottled, which could be next year really. It'd have to be something like a Bordeaux. Speak to someone who knows in a good, independent wine shop. Also could be expensive because you're looking at one of the big wine makers, and buying a case!
As an alternative to a moneybox I'm considering buying baby Godson something he can open and enjoy when he turns 18. I was originally thinking whisky but have since discovered it does not get any better with age. Can anyone recommend anything? Thanks (or should I say cheers?!)