Clean horizontal surfaces with a spray detailer. You won't need to clean the whole car, just the noticeable surfaces that catch dew or light rain and leave water marks. The eyesore places are the hood, trunk and rear bumper.
A clean windshield is a clean car. Glass is easy to clean and it sparkles like a jewel once you eliminate the haze and grime. Visibility is a huge safety factor, but a clean windshield also just makes you feel better about your car. When you're finished with the outside of the windshield, clean the driver-side window and side mirror, too. And for bonus points, clean the inside of the windshield and rearview mirror.
Take out the garbage. It's a car, not a dumpster. Pull up next to a garbage can somewhere and dispose of papers, food or other junk. Better yet, put a small trash bag in your car and empty it often.
Shake out the floor mats. When time is tight and you don't have a vacuum, you can simply grab your floor mats and remove all the gravel, loose dirt or sand. The mat on the driver side probably is secured, so you'll have to work it off the anchors first. But the other floor mats are unattached and you can simply just whisk them out for a quick flapping.
Clean the wheels and tires. The absolutely laziest way to go is just to use a cotton rag to wipe off the flat center section of your rims. If time allows, work the rag into the spokes or crevices. You also can use a brush for the hard-to-reach areas.
Clean anything you touch or look at. While you are in the car, you spend lots of time checking out the gauges, the dashboard and the center console. So take that microfiber towel you used on the car's exterior and quickly clean off some strategic areas inside the car. The plastic covering for the gauges is a must. Then, wipe the dust off the dashboard and sweep the fingerprints from the center console. Some experts recommend keeping car cleaning wipes in the glove compartment for convenient interior touch-ups.