While we can obtain many essential resources from agriculture, we cannot obtain them all. Some of the main objects missing are Tin, Copper, and Coal.
The tin and copper plants would most likely be very similar to ferru.
I was thinking the coal plant would be like melons, except it would drop coal.
Sorry for lack of tier+recipes and what not, they just tend to annoy me and Al can think of a better way to do it anyway.