Basically, I'd like to have a discussion of some various improvements to agriculture that pre-industrial humanity could implement, without too much of a stretch. Different under-utilized crops, crops that we've only recently discovered are useful, plants that could be domesticated with minimal selected breeding, earlier discoveries, etc.
For example, one that I'm quite partial to in my timelines is the idea of coffee being cultivated earlier in history, and the influence that would have on Indian Ocean trade networks.
Another example that I've recently been quite interested in is tagasaste, a very hardy nitrogen-fixing tree, native to the Canary Islands, which has, in the past 3 decades, become very popular as a fodder crop, mainly for cattle:
https://en.wikipedia.org/wiki/Cytisus_proliferus
Basically, alfalfa on a tree. This is the sort of crop that could result in large livestock gains across the world, particularly in pre-industrial/pre-fertilizer societies, and particularly in marginal lands.
There are others, those two should be enough to get the ball rolling.