Add additional ways to make criminal money besides just chems. A few examples may include

• Store Robberies
• Smuggling Deliveries, where you must place illegal contraband into your trunk and transport it across the map to different npcs or locations for larger amounts of cash.
• Vehicle Chop Shops. Its already illegal to steal car, why not add a few shops around the map where you can sell them for cash?
• Home Robbery, add alarm systems to homes and let players break into them to steal items from safes or items laying around the home, they can then sell them for quick cash at a pawn shop.