Let them know that you are very proud of their sacrifices for you. Just 2 words would be a good place to start. We read in the book of James that the tongue can harm us but in the Psalms we also learn that a kind word is like honey. If any man among you seem to be religious, and bridleth not his tongue , but deceiveth his own heart, this man's religion is vain. Words can hurt us to the core.
Words can also nurture our soul and spirit.
Unexpected acts of Kindness really do bless the receiver and also the giver. We know from the news and history that during and after almost all the wars the soldiers were shown tremendous respect, honor and appreciation. The pictures of the ticker tape parades and the sailor kissing the lovely young lady are permanently imprinted in our minds. Unfortunately during and after the Vietnam war we failed to show our service people the respect and honor that they deserved. I am sure that little extra effort will be very much appreciated.