When you combine your errands into one trip you save money as well as time. Frequent short trips with a cold engine uses nearly twice as much gas as one longer trip with a warm engine. A multipurpose trip also cuts down on the number of miles because you are not going home in between each errand. A little planning beforehand and you can complete several errands in a short time, your engine will be warm and more efficient and you save money.
If you can, try to stagger work hours so you are not driving during peak traffic hours. Use your most fuel efficient car. Talk to your employer and determine if he will allow you to telecommute or work from home so that you will not have to drive at all. You can also join or start a carpool or a ride sharing program. This will save wear and tear on your vehicle and cut fuel costs down to half or more, depending on the number of commuters taking turns doing the driving. In some urban areas there is a special lane, the High Occupancy Vehicle lane, for vehicles with several passengers. This lane is less congested which improves your fuel efficiency even more.
Another alternative is public transportation if it is convenient and available in your area.
Roof racks and rooftop carriers are super convenient when you need to carry extra items. Just strap them on and you get all the additional space you need. However, when you load up your roof you decrease fuel economy as much as 5 percent. The aerodynamic drag means your engine has to work harder and therefore, uses more gas. Put as much into your trunk as you can, reducing the amount you have to carry on your roof. And avoid taking anything that is not needed, especially heavy items. For every additional 100 pounds your fuel economy is reduced by about 1 to 2 percent.