For thoughs that live in and around cities.
It might be a good idea,check with local laws,see if ok,wink wink,to start planting in parks/cemetaries/swamps/abandoned fields etc:onion/garlic/chives ect.Best to do these starts in little bunches.
Different kinds of greens,mustard,card,collard,just scatter small hand fulls of seed.
Keep in mind that they will need to be watered so look nature springs/runoff ditches/in and around swampy areas.
Plus by doing something like this,if it is ok with laws in your area.
If you and yours were to be homeless,new trend,
seasoning herbs will be close by for feral cats/rats/dogs/birds etc.
Life is sometimes bland,so if you got the time spice it up.

I just watched some videos about something simular to this on youtube. I think he calls them survival gardens and they are basically hidden in plain sight. The Idea is not to have one large but many small hidden gardens that you visit as little as often and they are less likely to be looted.

S

Im having trouble finding a link. He illustrates the minimal amount of tools needed and locations that require the least amount of care. He also shows inexpensive ways to deter pests and camouflage the small gardens. It is generally geared toward the rural gardener but could easily be adapted to urban areas with parks, abandoned lots, etc. I also like a lot of Mel Bartholomews ideas on gardening http://www.squarefootgardening.com/

If I come across the videos again I will post the link.