Hopefully you knew him well. Something I never thought about when I was a young lad like yourself is when you have your own little peeps they'll ask you questions about their great-grandparents. They take a keen interest that I wasn't really expecting.
Be sure to keep some photos and remember some good stories to tell them. Write them down if you have to so they'll be fresh when the time comes.
but sorry to hear that bud. Try and remember the good times, memories help the sorrow, IMHO......and if you need to talk en such.....its a message board, but PM me