I should also clarify that I don't quite see the situation as a "charity vs. social justice" thing. That's why I think there can be room for both. Charity, whether random or intentional, can be social, just, and socially just.

In fact, I'd go further to say that social justice could be seen as a state that we can choose to seek out, as John you point out. We can seek to "phase change" from socially unjust to socially just in any of our transactions, depending on the conditions (the 'enabling environment'?) from charity to commerce to communication.

So for example, you might choose to consistently give to an orphanage that pays sizable administrative fees, or choose another where more moneys are put to direct costs of child care, education, etc. This could be the result of a 'social justice' motivation (or not), although in either case giving could be purely charitable.

Also, I am not certain that some of the activities you list, for example "collective bulk buying groups" are social justice. They could be about more base values, like optimizing purchasing power, couldn't they? In the same way, community gardens aren't inherently about social justice (it would be interesting wouldn't it for example to measure the average household income of people tending to community garden plots in cities). Some of the other motivations/benefits could be social, getting ones hands dirty, feeling "close" to the land, exercise, sense of "independence," etc.

The question might be, "What are the ways community gardening can be run that serves social justice?" or some such...

Where I think your argument really sings is, "How you frame the issue shapes the solutions you choose. A charity model view might say, these people are lacking food, so we will provide food. The social justice view looks at what are the conditions that cause them to not have enough food."

You could explore that more - perhaps with an eye toward the kinds of questions that, when answered, help the reader understand how (if they desire) they can transact the state change "from" charity "to" social justice."