Suggestion for a change how farms improvements work, replace the current farm with a farm improvement per resource you can farm(corn, rice, melons) but you can only make then if you have the appropriate resource. This will prevent empires from loosing access to grain if they loose there only bonus resource providing it.
Another thing that might be done is have the map start with improvements like wild rice that can be turned into grain farms by workers and/or have wild corn improvements spawn by events.
If there are spawning food improvements deer, horses and other grazing animals can destroy them to gain some xp.