My first choice is the Egyptian Onion [which is more like a scallion than an onion.] It can pretty much take care of itself in most situations. You can use it like a scallion but you can also fry up a batch throw on a little sesame oil and eat it like a green vegetable. I learned this from a Chinese lady who served me some garlic chives that way.
I thought I should try it with the Egyptian Onions and it worked out nicely.
I have to say I'm a guerrilla farmer as well as a guerrilla gardener so my perspective is a little different from someone who expects nothing- but the fun of it- from what they plant. Once people realize that there is something they want regularly growing on the "commons" you are in a vulnerable situation.They may take it all! I try and stay ahead of them with "diversity' - a- real hodge podge especially plants not commonly known to my culture. Bulbs and root crops are good since most people don't like to get dirty
also there is a world of herbs that have medicinal value that most people think of as weeds.And my last resort is to plant seeds of things that require a year or two of growing before they are truly useful. garlic chives for example. Then in the second season I can move them to a more secure area.
Like the lady says,
Green Blessings to you.