The idea is to show you have the skills the next employer will need, so first you have to identify what those skills would be. For example, if you want to be a manager, the employer probably will want leadership, communication and problem-solving skills, along with any technical expertise required in that industry. Pull out agendas and meeting notices from those activities. The final step is crucial. Now, you have to choose material for 10-20 pages in your portfolio and organize it to tell a story.
Captions are important, because they explain the relevance of each item.
You might want to arrange the pages in sections and use tabs to make them stand out. A table of contents is helpful, too. After you have your portfolio, practice using it in mock interviews. Croonquist has become a believer, based on the successes of people she's advised. One student won an interview for an internship and put together a book describing her work on campus and volunteer experiences.