I use the term "guerilla" here not so much to mean unsanctioned -- though my small plot is -- but to mean occupying unused space. A small section of parking garage roof, which is right outside my first floor window, is the perfect location for a little intervention. The two small poles you see are supporting Roma and grape tomato vines.
I also have a dwarf blueberry bush, some basil, and both zucchini and yellow squash, all within watering distance of my living room windows.
A neighbor (or a group of neighbors?) has planted a little food garden in the corner of our (quite large) backyard, adjacent to the worm bins. She has tomatoes, herbs, peppers, and leafy greens in the ground and in pots.
She has also used buckets to plant carrots and Yukon Gold potatoes
Admittedly, our building has a love for decorative gardens and is located on quite a large parcel, so this type of garden fits well. On the other hand, some apartment residents may not have this sort of space at their disposal, and that's where the former type of garden might work better. And if neither of these options is available, there's always the ROW Garden model, or the full parking lot takeover...