Growing your own food is work; where is the retirement plan? What if you're not able? Even if you are, many people want to do things other than farming when they retire.
It feels like the ultimate defeat: what have I achieved in this lifetime of work, when I'm reduced to land-to-mouth existence, like an ancestor tens of thousands of years before me? Where is the progress?
Theft is a problem in community gardens. If you just grow enough to sustain yourself and someone steals your produce, you're back to fucked.
There are simply too many of us to revert back to an agrarian society. We have to create food at a very large scale. Which means we have to become better at sharing it.
Like it or not we're all in it together and we're doing kind of a sucky job of it right now.
Healthcare and education are areas where a common option could make a major difference in people's lives. But I think the "community" has to be pretty large to make a meaningful impact.
Hunger is further down Maslow's pyramid. You can't even begin thinking about things like education until you are able to adequately eat.
Another approach is to build security through self sufficiency and community based initiatives. For example, growing your own food wherever possible, or community gardens on common land.
There is a long list of examples and ideas where future security, defining that as decent quality of life, health and education, doesn't need to be based around monetary wealth.