Actually, they don't! Only certain plastics contain BPA and food-grade plastic bags are not among those. It's the lexan-type solid plastics that contain BPA, and most of those have had the BPA-producing materials phased out (especially since they can't be sold in Canada).

On the other hand, the freezer bag companies do not recommend boiling in their bags. There are bags sold that can be used for boiling. If you are really worried, you can get these for freezer-bag cooking. They are, of course, more expensive. However, freezer-bag "cooking" does not involve boiling in the bags, but just pouring in hot water. Remember that the normal process of preparing vegetables for freezing involves blanching the vegetables for a minute or two and packing them in the bags while scalding hot. Freezer bags are designed to take heat, even if not boiling.

By the time you turn off the stove, remove the pot from the stove, make sure the freezer bag is still open and stable, pour the hot water into the bag and stir, the water is well below the boiling point. More like 190*F, and definitely less at high altitudes where the boiling point is about 190*F.

We really should call this process rehydration, not "cooking," but of course the latter term is easier to use even if misleading.

Note that most of the foil bags in which you rehydrate commercial freeze-dried food have plastic linings. Most metal water bottles (what my daughter insists on using) also have plastic linings.

I hate washing dishes so much that I figure that nothing in the plastic bags will harm me as much as the psychological damage of having to scrub dishes, not an easy process in camp!