Summer squash (zuchinni, crookneck) are prolific producers, and their fruit can be put up fairly easily. They will grow in milder climates, and they don't have runners like winter squash, cucumbers or melons do. They are quite bushy. With a family of four, I planted 3 plants one year in Walla Walla, and I had to give away quite a bit because I was filling my freezer with them and we were getting tired of eating them every day.

Carrots are also a good crop. The fruit is durable and stays fresh as long as it stays in the ground through and past the growing season and into winter if you keep them a little insulated. I've pulled carrots out of the ground in December that were crisp and delicious.

Spinach can be prolific in northen climates, especially with lots of nitrogen in the soil. The plants will quickly bolt to 3 feet or more in 30-45 days with a prodigious number of leaves. We used to pull spinach plants out of our garden as a kid every week and mom would have us take them to all our neighbors.

Chard/Kale are good second crop plants, meaning you put them in the garden in places where other plants have been harvested, late season summer, and they will stay viable into the winter. Not quite as durable as carrots, but we've picked Kale in early December, and lots of it.

Pole beans will generate a lot of fruit on a few plants if you have something for them to climb. We got over 50 lbs of fruit off one 12 foot row in one season.

YMMV