This is a great question! My career in marketing has involved living in what I affectionately call 'cube-city'. All the little minions like myself are crammed into the smallest possible working space and impossibly small storage.
Working in marketing involves working on multiple projects at once and most of them have sub projects. For example, a campaign may include direct mail, email, internet, signage and social media. This means working with nearly every cross-functional group in the enterprise: Finance, Legal, Graphic Design, Video Production, Accounting, IT, Business Development and of course outside vendors and agencies.
Maintaining the project space is critical due to deadlines and because of the limited working space. I use manilla file folders to keep the chaos organized and on a step-rise wire file holder on my desk. I may have as many as 2-3 at one time.
Each independent piece of a campaign has its own folder. That way I can track the development, timelines and budget to ensure the project is on track. Once the project is complete, all folders are kept together as a historic document and place in a hanging, expandable file folder.
This keeps my desk organizer and keeps the information within arms reach if I need to answer a question, grab it for a meeting or call a vendor about a concern.
I hope this is helpful.