I use folders for images and files.
I have folders for each department for email templates, landing pages and images:
Events
Marketing
Research
For images and files I break it down whether it's an image or a PDF file and they go into the following folders
By publication, bookstore, events, advertising, sponsorship
Subfolder:
images for promotions
images for renewals
images for conversion series
images for publication fulfillment
PDFs:
By publication name
Advertising
Events
Snippets is broken down by:
Marketing footer
Events footer