You will most likely only have to deal with localized emergencies - such as hurricanes. In this case a 2 to 4 hour drive will get you out of the zone and you can get whatever you want. Gas, Food, Drugs, etc.
In the case of a national disaster - nuclear war, germ warfare, etc, then you just pick up one of those guns you have stockpiled and go get you some. Where from? Who knows.
Now the problem will be that before you need meds you will need food. Grocery stores will be out in 2 days tops, and I do mean tops. Since this is about meds I will not go further than this on food. Same with generalized drugs.
If you need the meds in question to live, then you need to look into ways to make them or something close enough (and it may be crude) to keep you alive. You can stockpile food - but stockpiling drugs is almost impossible with the laws we have. Look for alternatives to the medicine that can be found in nature and start growing that plant only found in southern Brazil...
If it is really specialized then read up on Darwin or get a Chemistry degree. Talk to a chemist, get to know your neighbors and their abilities.