Bring your host family something that comes from 
your hometown.  Like if there's a special kind of 
cookie or packaged food that your town's known 
for, bring that.  (Cookies/sweets are popular 
souveniers in Japan--this shows up in a couple of 
anime shows, btw).  Picture books about your 
town/area are also good.  Essentially, something 
small but unique, something they're not likely to 
get anywhere nearby.