Reusable bags are a fantastic idea. They cut down on waste and occasionally add some panache to the chore of buying groceries. Like anything that deals with food, it's a big deal to avoid cross contamination when using your grocery bags and to make sure that you are transporting things in the safest way possible. First of all, make sure you can clean your bags effectively, and that they aren't made of a material that can't be machine washed and/or bleached. Once you have your bags and use them regularly, try to wash them at least every few shopping trips if not more often. Another thing to keep in mind is to always bring multiple bags with you. While most reusable grocery bags are pretty sizable, you should still maybe consider keeping one exclusively for meats and eggs (if you eat those) to avoid contaminating foods you might eat raw or without extra cooking, like fruits and vegetables. Another thing to keep in mind when using your reusable bag is to make sure you aren't putting things like eggs or breads at the bottom or middle of your bag, as they will probably get crushed. With all of this in mind, happy shopping!
For a report on the potential health risks that reusable bags can pose go to http://content.usatoday.com/communities/greenhouse/post/2010/06/shopping-bags-health-risk/1