Hi there,
It is a very nice gesture to bring your student host a small gift. After all, these people are allowing you to stay in their house and saving you some money. Something edible is good but you might run into dietary restrictions. Something for the house like a nice photo frame might be nice. One of my applicant visitors gave me an assortment of "Post-It" cubes which was very useful.
If you can take your student host out to dinner or pay for some "Take out" of their choice, you can substitute this for a small gift. If you do not get a chance to do anything, you could mail a gift certificate to Starbucks or something like that back to your host after you leave.
It is just another way of saying "Thanks" that shows you have some manners.
njbmd 🙂