Gonna keep it short and sweet. Considering most of the GTA V map is county and hillbilly land, I think something that would really build on these is an alcohol brewing script. Like you could be a farmer if you guys had a semi in depth farming script where you could grow like small fields of corn in your back yard if you purchased the right properties, or you could straight up buy corn of something like a storage depot. You'd then be able to either have a small personal brewing kit at home which you could upgrade and have tiered system, or just buy some kind of factory/building dedicated solely to shining. So tier one would be like a crappy 10l bucket used for brewing small amounts, it could fit in your house.
Tier two would be bit larger and so on until you get to a largest tier which would indicate a level of mass production.
This could also be implemented for beer production, wine, vodka and so on. Something to actually create an RP industry in game which is completely realistic to have in a state like San Andreas.