Please help. need ideas for a very very special gift something to rember some1 by. plz help?

ok, so my boyfriend of a very long time is going to military school and he is going to be gone for 6 months, im not going to have much contact with him during these six months, we can write letter back and forth that's it i cant see him or anything, and he said that it would be cute if i got him something small that he can keep with him during this,like something to remember me by. and i have no clue what to get him at all! plz if u can think of anything that would be very helpful, caz he only have 2 more weeks here =( and by the way plz don't say a pic of us together caz he all ready haz one.