Here are the things I included in my missionary survival kit:
a Nerf gun - for the girls you don't like
gum and Chapstick - for the girls you do like
sour gummy worms - for after a date has gone sour
a journal - for the new memories you make
Itunes gift card - to catch up on the latest tunes
starburst - don't let anyone treat you like you are a yellow starburst. You are a pink starburst.
m&m's - for being such a marvelous missionary
Reese's Peanut Butter Cups
Skittles
I didn't have any good ideas for the skittles and peanut butter cups so I just included those in the basket.
You can also include a list of movies they have missed while they were serving and some movie tickets.
Obviously you can change this for a returned sister missionary but just have fun with it.