But how gross are those grocery bags?
More and more shoppers are giving reusable totes a try, but some health experts worry we're at risk for food borne illness.
To find out more, we took a sampling of bags for lab analysis.
We tested the bags at a lab in Pasadena for aerobic plate count, which will give a general count of all the bacteria that are there, and we also looked for some pathogens like listeria and salmonella.
The good news is that tests revealed our bags were free of listeria, salmonella and E. coli.
But when it came to general bacteria, our bags were full of it. Counts ranged from 15 to up to 450 CFUs.
What are those, you may ask?
"Colony forming units," said lab tech Regina Norman. "That's how bacteria are measured."
Norman says three things bacteria thrive on are food, like what's left in the bag, water or humidity and temperature - a perfect storm for all in your car's hot trunk.
"Bacteria love that heat," Norman said. "One hundred degrees. They love temperature and they will multiply very fast."
Ironically about usage, 97 percent of the people who use them say they never wash them, yet putting them in the laundry can get them just as clean as your clothes. If they're not machine washable, use hot, soapy water.
Dietitian Ruth Frechman says put any meat in plastic before putting it in the bag and suggests sing a color code system.
A different color for meat, chicken and fish, and another color for fresh produce and ready-to-eat foods.
In addition, to avoid cross-contamination, keep grocery bags for groceries, not your gym clothes, pedicure flip flops or sports gear. Give them their own bags.