Sap Run
The longest haul on the island: south field, east lab.
Where to go
Poppy field — the far south, past the Casino and the Restaurant. Farm Lab is in the far east beyond the Jungle Lab — a 50 km drive.
What to gather
Collect Poppy Sap from 11 bushes, no tool. You also need Water, an Empty Glass Bottle and Naphta (Chemical plant or El Cocodrilo).
Poppy Sap 
Water 
Naphta 
Empty Glass Bottle How to process
Farm Lab: 8 Sap + Water → Opium Ball; 3 Balls + Naphta + Bottle → Heroin Brick; Brick → 6 Bags.
Opium Ball 
Heroin Brick 
Heroin Bag Where to sell
Bricks ($3,500): El Cocodrilo. Bags ($720): street dealers.
Heroin Brick Heroin Bag
TipThe margin is good at every step. Plant Poppy pots at home to skip the drive to the south field.