I've got mine a groom box and in it I'm putting my boudoir shoot pics, an engraved hip flask with his favourite brandy, some groom socks, a groom journal, an album of our engagement photos, a card and a few other bits and pieces (can't think what they are at the moment).
I'm making it really personal so that it calms his nerves and gives him something to look at the night before or on the morning of the wedding.
Tied the knot 9th June 2012!