Here are maps to help you find various things. These are from the in-game website, Use a computer in-game to visit the site and find the same maps. Don't try it on the internet here, as it won't work.

Flying RatsFlying Rats Flying Rats 2Flying Rats 2 Friend ActivitiesFriend Activities
Health PacksHealth Packs Hidden ArmorHidden Armor Hidden WeaponsHidden Weapons
Random PedestriansRandom Pedestrians Stunt JumpsStunt Jumps Text Message CarsText Message Cars