Double Progress
Connect two controllers to the PlayStation and visit your girlfriend's house to go on a one-player date. At the end of the date, activate the two-player icon by the door before it disappears. When you enter free roam and receive a progress reward for having a good date, it will be a much larger reward than if you had just completed a one-player date. However, activating this glitch not stop you from losing progress if your date went badly.
Girlfriend Bonus
Restart the game after having dated a girl who provides you with a bonus. Even if you do not date the same girl, you will still get the bonus that you received previously.
Girlfriend Distraction
Take your girlfriend with you while you are attempting to take over a gang territory. If enemies are being hostile towards you and you kiss your girlfriend or give her a present, the enemies will freeze until you threaten them again. You will be able to collect weapons and items in the area without being attacked.
Cars from Girls
Date a girl until your relationship is at least 50% to get the keys to her car. Helena has a Bandito; Millie has a Club; Denise has a Green Hustler; Michelle has a Monster Truck; Barbara has a Ranger, and Katie has a Romero.