Dude! Dude! Dude! Are you ready for this?.... A wall mounted urinal preferably like the ones they have in the boy's room at school!!! (For an added touch, put in a couple of "mints") Then when a girlfriend moves in you could possibly convert it to some Buddhist shrine and she can do her Yoga in front of it.
I got this. In my man cave I had a pc with music playlists in my media player, ( desk top with kinda nice speakers, 17" screen), internet access, a tv with a XBox, (I only ever really played one game. We had epic Tekken sessions), a steel tip dart board with 2 sets of darts, a decent sized fridge, not huge, ( here's a tip; always put the girl drinks on bottom shelf and way in back. This is just courtesy for your bro's.), a microwave, and a sink, like a decent bar sink, and a way for people to take a piss.