I think potatoes generally get the most calories per square foot. As an added bonus they're incredibly high in potassium on a per-volume basis, compared to other foods.
You can also squeeze more calories out if you plant crops with more than one edible part. For example, eating the seeds out of your winter squash. Or, if you take the parts that can't be eaten by humans and feed them to livestock, like when you feed fruit prunings to meat
rabbits or table scraps to a hog.
With legumes, climbing vines produce more than bush plants, and different varieties produce different amounts. I did a comparison of 6 different pole beans last year, and found that Good Mother Stallard produced 3-8x more than the other varieties, for the same amount of row space. Your climate might be different, so I'd suggest doing a controlled test to see which variety does best for you.
Also with beans, letting them ripen all the way gets you more calories than picking them as green beans. Green beans are tasty, but they're low in both calories and other nutrients when comparing on a per-volume basis, so they're essentially filler.
I'll add more as I think of it.