I think this is maybe the question that I really had in mind (in my post yesterday).
A question like that, though, makes it seem like all you need is the short list of topics or the top Ten list.
Isn't learning about plants, gardening and the natural world (anything you're interested in, for that matter) a lifetime (or continuing) pursuit?
I like to end presentations about wildlife gardening, or gardening with native plants, or vegetable gardening with this quote from Thomas Jefferson. It's often quoted, as it deserves to be.