In the Grand RP in the gym there is an opportunity to automate the process of increasing the backpack. First you need to go to the simulator and press «e». Then run a macro that will allow you to relax, and as a result your backpack will become bigger. It will have additional items that will get into your menu. Exit the menu so as not to interrupt the process, and you can continue to earn money for investments. Don't forget that this is only possible in the gym located in the Grand RP.