Deciding to go green is a wonderful thing to do but you do have to remember to think and look at all products and realize that not all containers and plastic bags can be re-used safely.
If you must use a microwave think about the containers you are using. Take for example containers such as yogurt cups, butter tubs, or even microwave food containers these are meant to be used only once. Some microwave containers may be made for multiple use; check the container to see if it states "multi-use" on the packaging.
You can, after washing, reuse them for "containing" items such as buttons, paperclips, nails, etc., not for reheating as the plastic will break down and who knows what is seaping into your food.
As for plastic grocery bags, you can reuse these bags but be careful with the types of foods you are carrying in those bags. If you carry meat in those bags and later reuse that bag to carry other items you may risk cross contamination. Consider using cloth bags that can be washed inbetween uses. Cloth bags are much more stylish and why not show off your sense of style and imagination.
Now to styrofoam: we all like to order take out food every now and again, wish the restaurants would use something other than styrofoam, but alas that is a whole other issue to tackle. Do not reheat food in styrofoam as it melts rather quickly and may give off noxious fumes.
Going green does not have to be a health risk but please do "think" when going green.
Check out The Green Guide for Everyday Living:
http://www.thegreenguide.com/
Here is a piece on BPA and plastic containers:
http://www.uabhealth.org/61158/
