I've been in the same boat. My resentment just built up over years, and for what? It just made me seem like an uptight arsehole. And I probably was too.
Looking like I'm working used to be a (minor) concern of mine, but I'm more focused if it doesn't enter my mind.
Charge for your time. Don't stop the clock for meetings, short breaks, toilet etc. Lunch is debatable. If you go for a short lunch, with your work colleagues, then I'd probably bill. If you like to get out and clear your head and go and hermit somewhere for a full hour, I'd say probably not.
If there are weekly perk-style activities that happen in-hours (Table-tennis, multiplayer games, etc.,) bill them. Otherwise your boss is just making you stay in the office playing vidya for free when you could be going home to your kids. If an after-work activity starts early, e.g. drinks at 4:30 followed by a team dinner at 6:30, I'd probably bill up until when I would have usually worked until (so 5:00 or 5:30).
One time I went and got coffee with some of my teammates in the cafeteria, and we sat around for a while and chatted. Later I was quietly praised by my manager for making that happen. Because his job was to make sure we could actually get along and produce work together.