There's a few things I've noticed make me really feel like a guy -- like, I was born a "cis-guy." I've noticed one is buttoning up a shirt over my chest when I'm wearing my binder: first time doing that I actually grinned it felt so awesome, then I ran my hands over my chest, haha.
At my last job whenever I'd walk a female co-worker out to her car because she was worried about a guy (one was basically being stalked, the other a bizarre regular that harassed her was hanging around outside) and giving them tips on the way, waiting until they were in their vehicle with the doors locked before heading back inside myself. My current job and my last job have/had me working primarily with girls/women, so whenever I'm working on fixing something or other or am asked to fix something I felt like one of the guys of the place. Also at my last job when I was had to deal with something because the acting manager/"person in charge" did not have the confidence or courage to do so I felt very much like the guy of the establishment -- especially when the guy I had to confront joked around with me during it (giving me a hard time but not being an ass) and then apologized after the fact.
Whenever I'm working on something mechanical, especially with my pops for some reason. Recently he had a flat he needed help replacing (he'd been in an accident a bit ago and wasn't able to get it himself) and when I said I was sorry, I'd help if I could (I had to work though) he said not to worry, he could ask my brother-in-law, but he knew I liked doing that sort of stuff so thought he'd ask me first (this was after I knew he knew, and he'd never really asked me before, so I kind of took it as his consciously treating me like a son even though we'd always done a lot of father-son type things together). Also when my girl tells me it kind of turns her on when I talk about vehicles and vehicle repairs.
Another recent one: while getting ready for work and trying to get a toy gun out of my nephew's toy fighter jet at the same time. Had to take it apart a bit in order to get it out and I imagined how many fathers probably dealt with the same thing before work, so the feeling sort of took root in me.
Being treated like any other guy by other guys in a conversation, especially when it comes to jokes.
When I'm asked to help move something (i.e. cabinet, large Tv) or I'm asked if I need help with something and I can decline, telling them it's not that heavy.
Recently on a walk when my ma asked if it made me scared or nervous to walk through the park in the dark and I told her no and she was surprised, even double-checked, confessing that it scared her a bit. I almost made a joke, but I behaved.

Okay, so that's more than a few...ah well.