I see several people responded with what they think should be a good gift, but imho such gift does not exist. He sells everything he's got so basicly the only things useful to him are cash and the stuff he's going to take. If it's a farewell party right before he leaves I'ld expect him to be prepared and have everything he wants/needs.
I think there are only two realistic options ask what is useful for him or give cash. In my perception everything else is useless in this situation.
Off course immaterial gifts a cheque for some kind of experience/excursion etc may have added value, but is close to cash.
