I'm not sure I should count these as hobbies as I never seem to spend much time pursuing them. But anyway, they're something to do when I retire.
Wargames - I haven't done any for years, but do visit the local shows and dig out my old rules and games from time to time. And none of that fantasy nonsense - I prefer mine with a bit of history.
Military History - Especially the American Civil War and WW1 Naval history.
Photography - As well as the usual holiday stuff, I try a bit of sport photography (some of my efforts are posted elsewhere on the forum). I used to be photographer for an American Football team, but someone else does that now as I'm doing other things, namely .....
American Football - As well as watching the sport (TV, Wembley, UK leagues), I'm on the staff of the Birmingham Uni team where I do most of their video filming, games and training.
Horserace Betting - I don't actually part with any money; I just like reading up on betting systems and trying to develop an approach of my own.
The Disappearance of Madeleine McCann - Yeah, I'm one of those conspiracy theorists.