I'll be doing an Internship in USA the following week, in UCLA.
I'm studying in Japan, where you should bring some kind of gift to your host professor, if nothing, for his/her kindness for accepting you as a PhD/visitor/etc.
I've seen this practice along Asian Universities (Japan, China, Singapore, India). But only in Japan professors may get offended if you do not bring anything.
A friend's professor is actually from the US (in a Japanese Univ), and when she have her a gift, the professor flipped and asked her whether this was some kind of joke or bribe, given that both of them were foreigners. Their relationship did not go so well after that.
Now, with this background, I'm a bit wary of bringing some kind of gift or souvenir to my host professor, since I'm pointing towards a postdoc in the same lab and I do not want to cause the wrong impression, but I do want to show some form of gratitude, since the Professor payed for all my expenses (lodging and airplane).
A better gift would be to take the Professor out for a really nice meal - then you can express your thanks in person, and show your appreciation by ensuring that he has a great evening.