Originally Posted by
Often1
It seems clear that they don't generate the need for a third item
I don't see where you're getting that. Under the ACAA, medical supplies are not counted in your carry-on allowance. All you have to do is have a bag that contains only those medical supplies.
If the medical supplies involve liquids in excess of the 3-1-1 limits it must be declared prior to screening.
Here's the TSA page on diabetes.
http://www.tsa.gov/travelers/airtrav...al_1374.shtm#3