F.M.
I hear that all the troops just GOBBLE up chocolate. So - a Snickers/Twix would be my vote. Or M&Ms to share. I am told that they don't care if it melts - they don't get chocolate over there (due to the melt-factor) and they lick the wrapper b/c they miss it so much.
Starbucks instant coffee mixing packets
Lip Balm
I sent an Easter package to a troop overseas - here was what other moms suggested I send to him/her in the care package: http://www.mamapedia.com/questions/18403374285755449345