i have 2 ideas. one is to give your gang allies commands, such as “follow me”, so when you get into a vehicle, they will follow you, and sit in the passenger seat, turret, etc. this way, you can go driving in the car/boat/plane/helicopter of your choice with a buddy.
my second idea came from being annoyed at the fact that vehicles i bought off the black market would disappear if i walked away from them. i think it would be a good idea to make it so these vehicles will last until being destroyed (if so, i think putting a limit on how many vehicles you can have at a time would be reasonable)