Challenge: come up with plausible, widespread/dominant agricultural systems that are the most divergent from OTL's widespread/dominant systems of annual cereal crops, annual root crops (potatoes and manioc) and grazing domesticates (cattle/sheep), browsers (goats), and omnivores that can eat scraps and garbage (pigs, chickens).
You can meet the challenge by coming up with a plausible reason that an OTL area that was mainly cereal-growing, e.g., relies mainly on a tuber in TTL.
In 1493 Mann speculates that much of the Amazon was deliberately planted perennial trees that were about as far from being monocultures as possible, many different useful species per acre. Could that have become more widespread, or could something similar have occurred elsewhere?
I've also read here that European cattails had possibilities as a swamp crop, which would certainly be a change from OTL. Northwestern European irrigator societies would be very different.
Some other possibilities: mariculture, either of animals or plants. Insect raising. Animals as harvesters or food retrievers. Crop succession, where you plant several varieties at once with the slower-growing kind meant to eventually choke out the faster growing. Fungus, maybe as the main way of dealing with scraps or indigestible plant matter? Parasites or fungus as a way of controlling animal or insect behavior. Flying birds. Bats?