I can't say that I have an elevator (or as they are called here in Australia "lift") speech ready to go. It depends a bunch on the situation, and who I am talking to. Whoever I am talking to, I try to get in the major points that have been mentioned prior in this thread.
As a former FLLer, I agree that FLL helps you with public speaking more than FRC does. I think one of the reasons for this is that FLL is easier to explain. There are two reasons for this. One, you can have a demo of FLL going semi-easily all you need is a table and robot. While the table might be difficult to get to a location it is possible--or you can just bring a portable table!
The other reason is that FRC is difficult to explain. I find myself rambling about alliances... and weight/height restrictions... and selection processes... and doing conversion from english to metric units... (I currently live in Australia) and explaining the size of the competition... and who Dean Kamen is... etc!
I have also found that it is harder to explain these things in a foreign country, since most people here have no concept of FIRST at all. Most people who I talked to in NH, had somewhat of a clue what FIRST was from the media attention GSR gets.