My sister and her boyfriend are visiting for christmas.... I don't know what to get her boyfriend! he's in his twenties if that helps.
Giftcard for music (iTunes) or a visa gift card.
i would get him a gift card or some money so he can get what he likes
A watch is always a good gift. does he have a phone?
ask your sister.
If you have the lottery where you live, a nice key chain and scratch-off tickets.
Big bag of candy.