I'm in a zone 5/zone 6 area, depending on the weather patterns each year off the coast. Gypsy peppers are the way to go. They're a sweet pepper and they don't get very large, but man, the plants are productive and they can withstand cooler temperatures and short growing season well. I've had no luck with hot peppers so I depend on family in New Mexico to ship me green chile every year. Even if they grow, we just don't have the summer temps for them to get hot.
Kale, most early tomatoes, most cherry and plum tomatoes, broccoli raab (never had luck with regular broccoli), garlic, beans and peas of all types, brussels sprouts, and spinach all do well. Root crops do excellent -- potatoes, carrots, onions, radish, shallots. Note on onions -- make sure you grow the right type! I'm in the north, so long day onions perform best because of our short summer nights. If your summer days are less than 14 hours long, plant short-day varieties. Melons do okay if I plant baby varieties, we don't have a long enough summer for a 20 pound watermelon. Cucumbers and squash go insane, but they do just about everywhere. Small fruits, including strawberries, blackberries and blueberries do well. We also grow hops for home-brewing, but be cautious if you have a dog (highly toxic to dogs), plus we are in west coast hops central.
I grow a few things year-round in a coldframe -- carrots, lettuce, kale, radishes and some of the less hardy herbs like rosemary. My cold frame is simply a raised garden bed with with a discarded glass door on top and plenty of straw mulch.
If you have a short summer, starting seeds indoors is the way to go. I rig up a bookshelf with those under-cabinet fluorescent lights, nothing fancy. The rest of the year I take the lights down and the shelf holds books. I make newspaper pots from my neighbor's recycle bin contents. They're free and I can transplant without disturbing the plant roots. To further save both money and a trip to the garden center, I plant seedlings in my homegrown compost, after sterilizing it in the oven.