Or, you could give nappies. These will be special as they will be the first nappies they will use when they have a child. Or, as a humorous gift, you could give XXX underwear with a note saying "use after 20 years... keep fit, or this will be your size...". You can give the catalog of a superstore in wrapping with vouchers. But remember: a gift box is an outdated gift, so be prepared to get funny looks when you give such a gift.