Steve's twenty-one years old and convinced that he is a failure.
All his mother ever talked about was how she couldn't wait for him to get married and give her a beautiful daughter-in-law to gossip with, and all his father talked about was how he wanted Steve to join the family practice and be a big shot lawyer.
Steve is interested in marriage, but the person holding his heart isn't exactly his mother's vision of a perfect partner, and to be entirely honest, Steve is willing to go through every single end-of-the-world fight again before he becomes a lawyer. He hates arguing, especially about topics he isn't too passionate about, and he's been more interested in cooking ever since his parents started leaving him alone so often for their "business trips." Because of all this, Steve really believes that he's some failed attempt at the perfect child, and he hates himself for it.
***
When he starts making lunches for everyone, it's mostly to calm himself: he can't follow every single person in his found family around all day, but he can make sure they've got plenty to eat, that they know he cares for them. It's not much, but it quiets the voice in his head (suspiciously Richard Harrington-like in both tone and word choice) that tells him he's being ridiculous or that packing a lunch for all these people is an embarrassment to the family name.
Everyone loves their personalized lunchboxes, so much so that Mike "lets" Steve make him lunch, too, after only a week. (It's packed with high-calorie finger foods, all of which have textures that don't make Mike want to scream. They're usually shaped like knights, swords, and shields) Steve's pretty much set for life, anyway, since Hopper strong-armed his father into leaving Hawkins back in '83, so Steve is happy to spend his time and money making his family happy.
Erica is the one who notices how much Steve loves to cook and actually DOES something, though. She demands a certain quality to everything she's involved with, and she's never shied away from telling someone they needed to step up, but she never once has a negative thing to say about Steve's food (the only complaint she had was with her first lunchbox: not enough food). It drives her actual parents crazy, that Steve can get her to eat anything he makes, when Erica has gone to bed hungry or fallen asleep at the table because she refused to eat something her parents made.
All this to say, it's Erica's doing that Steve is signed up for so many events. She doesn't even ask; if they need food, she volunteers him, and Steve can't say no to his Kids, so he always comes through. Steve is the envy of all the PTA bake sales, school dances, and even Parent-Teacher Nights with his cooking, and Erica is his number one promoter. She even bullies Hopper into signing Steve up for a booth during the Hawkins Fall Festival (in '87, since the 1986 festival was cancelled because of the "earthquake"), and her Encouragement™ is how Steve ends up with forty batches of brownies, several hundred dozen cookies, fifteen pies, and a veritable mountain of other sweets packed into a small canvas tent one morning in mid-October. Erica doesn't do work unless it benefits her directly, but she spends all day in that booth with Steve, Joyce, Robin, and Argyle, manning the money box so that the other four can just serve treats. They make so much money that Steve buys their entire groups dinner (and if he leaves fifty bucks in the pocket of Wayne Munson's coat, that's just how it goes).
Steve continues to make lunches, but after the festival is over, he starts getting calls to his house AND Family Video, asking him if he'd cater, if he could make a dessert, if he was available MONTHS in advance for a block party. It's overwhelming, but people adore his food, and just that thought motivates him enough to start booking each request.
By the end of January 1988, Steve has raised enough money to seriously look into starting his own business. Numbers make him sick (not really, he just hates math), so he asks Joyce to help him with finances, and before spring break, Hop's is up and ready for business. (Hopper cries when Steve tells him that he's naming his bakery after him- that's his boy and he's bursting with pride and love for this idiot kid)