Difficult to say what someone else should have in their man cave/poolroom. But if it were mine and I could put in it what I wanted:
Different years of Jeep grills, with some low output LED lights, so they don't blind ya
A couple of truck bed cut off's, so you can flip up for room, or fold down for comfortable seating.
A home made couch with a tailgate insert in the back rest.
A mini fridge, or a full size one if you have the room
A coffee maker and supplies (for those who know me, will understand)
A ping pong table top to lay down on the pool table for extra activities
As large of a flat screen as you can afford
A sound system that would also work with the TV, with a killer selection of music
A shitter, so you wouldn't have to go out to , go!
a wood stove, or even propane logs just for effect. Nothing smells better than a pot of soup cooking or some roasting peanuts.
Some cabinets to hold basics, solo cups, bowls for soup, and so on.
A galvanized trash can
high mounted shelves around the room, for what ever you might collect.
disco light, black light, florescent posters LOL
Any other "manly"(tacky) accents to keep the kids and wife out