I'm not sure of your general location, but for gardening purposes, I'll assume somewhere in the southeast or mid Atlantic.
For low maintenance, my first choice would be bush style green beans. A small package of seed (60 total row feet) gave about 20 gallon freezer bags full plus all we cared to eat fresh during the summer.
Lettuce is a good early crop, but really needs to be in early. Once the weather gets hot, it will "bolt" and go to seed. Once it does that it doesn't taste as good. Never had much luck with spinach. Can't seem to squeeze in enough good growing time between tilling and too hot weather.
Zucchini and summer (yellow) squash also don't need much attention. I prefer the bush types for these instead of the running vines, but that is a function of space in my garden. They are prolific producers if they are happy. One or two or three per plant per day.
Also Okra. Clemson spineless as mentioned above is a good producer. Just have to harvest frequently so the pods don't get too big and the plants keep blooming and producing.
Onions (grow from sets, [little bulbs] not seed) and beets don't require much maintenance. Sometimes gnawy toothy creatures harvest some beets before we do.
Tomatoes require a little more maintenance, as they need to be staked or caged or otherwise supported. Many varieties to choose from. Peppers are easy as well. Lots of different choices, hot, sweet, red, green, yellow. As long as you wait until the soil is warm they do well. Planting out too early stunts them from the cold.
I don't do corn because of space limitations and the ease of getting much more than I could grow for a few $ at a local produce stand. And that stuff is as fresh as what I could pick. And its available over a longer time frame. Big growers do multiple plantings about 2 weeks apart, So they get successive waves throughout the summer.
What you should plant also depends on where you are and what you like to eat.
