Doing push-ups in your garage will improve all three Attributes only so much and saving up enough money for your own gym equipment takes time. The option to train at the gym becomes unlocked early in the game and costs $10 a session and lasts for however long you want it to providing you do not need food or sleep. There is a vending machine at the gym which you can use to purchase energy drinks to help you stay awake and snakes to help you ward off hunger.