Insulin and syringes are often available without prescription-but the insulin doesn't have much of a shelf life, especially if not refrigerated. (http://members.tripod.com/diabetics_world/InsulinRx.html)

It might be possible to reduce or eliminate the need for some medications by lifestyle changes-weight loss/exercise can modify the need for anti-hypertensive and anti-cholesterol medication.

There are some folks who have had success in using herbal/naturopathic/alternative/complementary therapies to reduce or eliminate the need for prescription pharmaceuticals.
http://nccam.nih.gov/

Or you and your physician may determine that your medications are doing as much harm as good. (http://blogs.wsj.com/health/2008/02/12/do-statins-dull-the-minds-of-some-patients/

When i was presenting my thesis about home-made IV fluid therapy, one of the more common responses was, approximately, "this is too difficult to attempt, so some people will die". Probably applies here, too.
On the other hand, many prescription medications are issued to treat maladies associated with the un-natural stressors that 21st century civilization inflicts on us. A good solid crisis reconfigures the stressors to a more natural array, and might be healthier than the 'normal' abnormality of modern life. Every er i have worked in has functioed better in a disaster than it has on a routine day. brings out the best in folks, and eliminates a lot of the bull....stuff.