I think you might start off by asking a question:
Who has a better idea of how the workflow should best be structured, the people who are doing it now, or someone who wrote a textbook who's never seen it before?
Things that make you go "Hmm..."
Not to say that there's no such thing as "best practices" for an industry, of course, but in a case like this, it's not pure accounting. It's food collection and distribution, so it combines elements of accounting with inventory control and shelf life. That's not a strictly accounting situation.
What I would suggest is you poll other businesses (and charities) who are doing this kind of work and ask if they'll let you sit down with them and go over how their workflow works. How do they do it?What pitfalls have they encountered, and how did they overcome them? Can they recommend a source of best practices?
And even though you don't want a COTS product, it might be worth going through their sales materials (brochures, samples etc.) to see how they've implemented the workflows. Much of the time, those COTS products have already done some of this workflow research and figured out what works.