This question is tricker than you might think. Most working class florentines did not write down what they ate, while extensive orders, recipe books and other documentation instead exists for the wealthy (especially the very wealthy).

You might expect that quantity and quantity of food is also mitigated by professional success - some guild members were what we might call prosperous businessmen, while others were poor journeymen and had to integrate their primary profession with odd jobs. Some had a steady income, while others might have an irregular or intermittent income. A younger professional might earn less income, while a more seasoned professional might earn more.

It’s also difficult to fully quantify how unequal society was: most “Bank Executives” (to use a modern phrase) would have been close relatives or trusted friends of the organization’s principal, and would take meals together with them as members of their inner circle. There was little in a way of what we would nowadays call “Middle Management,” and most staff attending to to the bank’s decision-makers could instead be reasonably classed as “Servants.” What we might class, “Managers” or "Ordinary Employees," meaning mid-tier staff drawing a salary, were not numerous and would have roles that would appear fairly unassuming to our modern expectations. Given the tasks they performed, it might even be surprising for us to find that at the time their roles were respectable or even prestigious. Fortunately for the purposes of our answers, one of the most detailed “Meal Diaries” in 15th century Florence is of one such person: Pietro Puro, a clerk working for the "Parte Guelfa," a sort of public-private real estate concern the Florentine government had tasked with managing property seized from exiled citizens as well as maintaining the city’s fortifications. Pietro’s main job was to act as a receptionist of sorts in the atrium of the organization’s headquarters, in addition to acting as a sort of gopher for the organization’s leadership (who, unlike him, would be of aristocratic or near-aristocratic rank, which in florence did include the leadership and most prosperous guild members, but were nonetheless a very different kind of person than Pietro).

But while we might not call Pietro a “Manager” as per our modern expectations, he was well-off by the florentine standards of the time: We have records that he commissioned fashionable clothes for himself and his family; and while he rented his home in the city, he managed to purchase a small vineyard and farmstead in the countryside. His job was also prestigious: While not tasked with significant decisions to make, he regularly interacted with his organization’s leadership, and he had small roles in religious ceremonies in which his organization was called to participate. He was also tasked with distributing alms which his organization gave to the poor.

So what did Pietro eat for lunch? It's difficult to say for sure - He takes pains to specify every time he has food prepared by someone outside the family (almost always on holidays) so we can assume he wasn't purchasing ready-cooked meals frequently. He either took his lunch to work with him, or returned home for lunch. At any rate, the midday meal would have been short, not particularly abundant, and it would occur sometime before noon. The largest meal of the day would have occurred when he returned home at sunset.

So that being said, what did Pietro eat? Well, he, his wife, and their two children ate a vast amount of bread. The family purchased an average of over seven pounds of flour a day (immediately delivered to a baker, specifically one Castellani to whom Pietro was a fairly loyal customer) which allowing for bread consumed by his wife and children, meant that Pietro ate about 28 ounces of bread each day (800 grams). Piero also occasionally bought barley, which could be made into broth or cornmeal, as well as oats which could be mixed in with bread flour.

Pasta, the Italian grain staple per excellence, appears sporadically on Pietro’s table. Often seasoned with expensive cheese, at this point in time it was considered an aristocratic dish which Pietro couldn’t afford frequently.

Vegetables were also a main dietary staple for everyone but the very wealthiest. Cabbage, garlic, onions, radish, mushrooms, and salad appears in copious amounts. They could be baked into pies or eaten raw seasoned with olive oil (although olive oil was expensive and Pietro purchased it infrequently - almost exclusively to season his salads, actually; as when cooking meat he seems to have preferred to use lard, which he actually didn’t often purchase, but seems to have obtained from the pigs he raised in his country home).

Did Pietro consume any protein? Yes, albeit sporadically, probably with a keen eye to when the butcher’s prices dipped a bit. He ate veal, considered the best meat, about twice a year. Poultry was consumed more frequently, with different varieties purchased in different seasons: Capon in the autumn and winter, and chicken in spring and summer. Goose was eaten in the winter, for whatever reason. As for red meat, while his employers and their aristocratic friends could and did eat it daily, Pietro never did. Seeing as he did eat more expensive veal, this could be a personal preference. Pork was the cheapest meat, but seldom figured in Pietro’s purchases possibly because it was considered low-class, although he when he did buy it he preferred cuts of salted pork.

The diet predictably also varied depending on church-mandated fasting days. Fish appears in these instances, although it also appears fairly consistently throughout the year whenever he seems to feel like eating it. Pietro liked to purchase his fish on the Ponte Vecchio (perhaps predictably) and interestingly seems he spent more money on river-caught fish than sea-caught fish (possibly because river-caught fish was fresher, while also being more scarse).

As for dairy, cheeses appear sporadically and were often purchased in the form of cheap crusts or rinds destined to flavor soups or pasta. Eggs also appear sporadically, even if the wealthiest would instead eat them very frequently, often on the advice of doctors who touted their nutritious benefits.

Rice, which in the following centuries would become a staple in northern Italy, appears infrequently and was almost exclusively used to pepare desserts, go figure. Fruit also makes rare appearances in Pietro’s shopping lists.

Interestingly, on special occasions like holidays, Pietro might purchase food and subsequently entrust it to a professional cook to have it prepared.

Pietro also drank more wine than we might expect him to. At the time, it was considered a nutritious beverage, although its inebriating effects were certainly well-known. Stronger and more flavorful wine was more expensive, while watered-down wine was exponentially cheaper. Tuscany produced a large amount of affordable wine locally, but a wide spectrum of wines from further afield could also be purchased (notably from Liguria, Corsica, and perhaps surprisingly, Greece). While it’s been estimated that as many as 300 liters of wine could be consumer per person (that’s about 80 gallons) it seems Pietro might have been fairly temperate, purchasing between 100 and 200 liters for his family per year (more or less between 25 and 50 gallons). But as Pietro’s employer was also a major distributer of alms (as most important organizations were) we can’t exclude that he purchased less wine than his peers because he was able to claim some the wine destined for charity.

Unlike comfortable Pietro, a day-laborer in the wool trade or some other occupation would instead be reliant in great part on the grain dole for their daily bread intake. This might be integrated with purchases of seasonal vegetables, while any protein purchased would have almost certainly been exclusively pork; which accounted for about half of all meat consumed in Florence (most of which would have been salted). But a laborer might also catch a break in their their employer would customarily provide them with a midday meal (if anything to keep them working). As an example, the architect Brunelleschi famously (or apocryphally) had food and wine hoisted up to the workmen up on the scaffolding of Florence's cathedral. In this case, they might nonetheless expect the working-class staples of bread, vegetables, and salted pork.

My main source has been the paper, "La tavola di un salariato fiorentino nel XV secolo," by Dr. Alessia Meneghin, which compares Pietro Puro's diet to the dietary habits of both both wealthier and poorer members of florentine society in the mid-15th century.