Well, that kind of answers the question, doesn't it?
If the officer has legal reason to search you, he doesn't need your consent.
if he doesn't, he pretty much has to ask you. It may not sound like a request (eg "I need to look in your bag."), but part of being a responsible, informed citizen is to know not only what your rights are, but when you can exercise them.
Seems to me this stop, question, and frisk business is just a riff on consensual searches.
The US Air Force has started including tax protester literature in the emergency supplies of their aircraft. If the plane crashes in a remote area, the crew is instructed to read the pamphlets and Goalie will be along shortly to rebut them.