A bottle of "Bordeaux" wine, if he is from France
He would appreciate to drink something else than water.

A "Grison nut cake", if he is from Switzerland
It will remind him of his Grison mountains but has the risk of making him more homesick.

A can of "Tomato Paste", if he is from Italy
To make him feel good to eat "Spaghetti Napolitana".

A real "Coca Cola, if he is from the US.
Because, if he is in some lost place, he will not need "Diet Coke"

A "Bratwurst", if he is from Germany
Then, even if he is only drinking water, he can imagine that he is at the "Oktoberfest".