The garage is often the place in the home where paints, thinners and other kinds of potentially hazardous materials are stored. Ideally they should be kept in a cabinet on the floor so that in the event of an earthquake, they won't topple off higher shelving causing spillage and a potential fire hazard.
Other heavy items and sharp tools should also be stored on lower shelving in cabinets where there's a reduced risk of them causing injuries. The plan should always be to minimize the risk of damage to vehicles or hazardous material spills.
If your water heater is located in the garage, it needs to be properly braced to the wall (see Water Heaters section for more information).