Be neat, complete, accurate and professional. They're looking for people with a lot to learn. If you have a lot of policy experience the internship is probably not for you. Excellence in your field is what they are looking for. Neatness and professional quality is a given.
Most people feel that two page resumes are taboo .
Some offices will be specific as to the content and length. If they don't give you specifics there probably aren't any. If you are unsure, ask a question to avoid making a mistake. They will probably read only a small portion of the sample if it is very long, but that's okay. They look less for content and more for coherency, sentence structure, grammar, spelling, and attention to detail .