The poster is used on exactly two occasions: the congressional reception and the poster reception before the final banquet. In neither case are you trying to teach science; you're trying to convey the very basic principles of your project and your enthusiasm for it. In particular, you want people to leave believing that they understand what you did, even if they don't. It really is not possible to go too simple here; you're not going to insult anyone by being easy to understand, and you'll be there to elaborate if anyone has questions.

The foamboard for this poster does not fit well into a suitcase. My strategy was to cut it in half and protect it with a box frame; then I arrived and found out that Science Service would have been happy to give me a piece of foamboard. If travel will be a struggle, let them know; they will probably be happy to provide the backing.