Tony leaves recorded messages on his computer periodically; they're labelled "Captain's Log" so that Pepper will think they are egocentric documentation of his adventures and not read them. He used to record one before every trip out, but it took too much time. Sometimes he records them in the air. Usually it's late at night, after a drink or five.
"Not dead yet," he says, grinning sharply at himself via the camera. "Today I rescued three kids and dog, prevented nuclear meltdown, broke three glasses and cut myself shaving."
"I never regret anything," he adds. It'd be weird if he told the truth about everything.
He never listens to them. He never deletes them. He uploads one to his armour and switches it out periodically, so that if someone finds it they'll know whose it is.
Nick Fury forms the Avengers. Tony gets drunk with Hank Pym and tries to seduce him with science, but it turns out Pym's already got it bad for Jan van Dyne. So they keep drinking, keep shooting the shit, and Hank doesn't seem to notice how Tony gets more and more touchy-feely, and Tony doesn't actually try to turn him on. Well, much. Well, not effectively.
Hank says, "Living like this, we never know if we're going to make it to tomorrow."
Tony says, "Makes you feel free, doesn't it?"
Hank says, "If I die tomorrow, I want people to remember me. Hank Pym. Not the man in the bizarre helmet and the skintight costume. They'll all see me as six feet tall and that's bad enough."
Tony says, "That's why you're a biologist and I'm an engineer. I want people to remember the things I make."
Hank says, "I want people to remember that I made them."
Tony records that conversation and saves it with the videos of himself. It's sort of like a promise, though Tony's not really sure what it is he's promising, or even who it's a promise to.
Jan's father gets sick. Bad sick. Instead of dealing with it in a healthy manner with Hank or Natasha or Thor, she finds Tony and gets him shitfaced, then has rough, messy sex with him on the garage floor. Tony tries his best to feel like a terrible human being afterward, but he just thinks about Hank on that same floor and maybe that they're all of them chasing the same failure, and then he needs another drink.
He has more than another drink, and passes out on the concrete floor. When he wakes up there's sun filtering in, and Jan left a .wav file on his desktop. Tony stares at it for a long time before going to get coffee. It's still there later that day, so he renames it and tosses it in the folder with the rest of them.
Jan's father dies. Jan doesn't call Tony, doesn't talk to him, barely looks at him. He sees her wrapped in Hank Pym's arms, sobbing into his shoulder. He thinks that it might be more like him to feel slighted or left out, but really he's just relieved. Jan deserves better than Tony Stark. Then again, pretty much everyone else on the planet does, too.
Tony gets drunk (again) alone in the garage, tries to explain to himself why he feels like shit, tries to shout things or cry or have some sort of catharsis, but he ends up just slumped in his seat, skimming through files he doesn't ever open. At some point he records just two words, and uploads them into the Iron Man suit. He doesn't switch out that message for a long time.
Thor and Tony drink a lot together, and Thor never gets drunk, so it's funny that Tony's completely sober when he breaks out the tiny camera.
"Say something people can remember," he says. "Something to play at your funeral."
Thor, predictably, goes on for half an hour. Tony's never heard anyone sound quite so inspiring while they talk about death.
Captain America paces like a caged animal when Nick Fury leaves him in the Malibu house ("We're keeping him off the radar right now. You're better equipped to keep him than we are. Got a problem with that, Stark?") and stares at everything with this weird combination of confusion and devastation. Tony has to remind himself that this man was only (in his mind) fighting in the second World War a few hours ago. The whole world must be completely alien.
He says, "Did you ever keep mementoes?"
Captain America looks a him for a moment, sussing him out, and then nods. "Some things a man needs to be reminded about."
"What about leaving messages?" Tony asks. He doesn't get any response to that, but that's because Captain America looks to be lost in thought. "You're new to the team, so you wouldn't know this, but we have a tradition of leaving messages to -- to ourselves. In a camera." Tony's lying, but not really, because it's not really but when he puts it like that, they all have left messages, some more than others. It won't hurt to add another.
Captain America stares at the camera in even more pronounced confusion, and doesn't say anything until Tony leaves. Even then, he just gets one word out before shaking his head and dropping the camera to the coffee table. He gets up and paces once more.
Tony uploads that video with the rest.