Free Weapons and Upgrades:
Perform the following glitch during a mission to get weapons and upgrades. Go to the nearest ammunition gun store and buy all you can carry. If you then kill yourself outside by dropping a grenade and return to the store you will notice that the items that you purchased before will be marked as brought and you will have the same amount of cash you had before you killed yourself.
Use the following useful glitch to instantly repair a damaged vehicle. To perform the glitch simply switch to another character and back while sitting in a damaged vehicle.