Potatos, sweet potatos, & yams are generally held as the most efficient for calories per square meter for single-crop plantings. Almost all tubers and root crops tend to be very forgiving and grow easily, although you should find ones adapted to your local climate.

Beans & peas fix their own nitrogen and can grow in poor soils. Very easy to grow, dry, and store, and makes for good cover crops and tillage. Need a good bit of trellising to make them grow vertically if youre limited in space tho.

Tomatos and peppers are garden staples for being easy to grow and high-yield, but are picky brat plants. Good for novice gardeners, because if they need something they’ll throw an tantrum, wilt till you fix it, and then perk back up in the hour.