After reading David Allen's Getting Things Done, I quickly moved to his system. For archiving and for "live" projects, the A4-sized file folders were great. But not for the stuff I wanted to lug around and "read and review". So I liked the hipster PDA idea (and a variant here).
But it looked tatty, and I was always rooting around in my bag for the stack (or "ring") of cards I needed.
Then I discovered PoIC. It doesn't mesh exactly with GTD or hipster PDA, but I like it. One thing I like about it is its analog (versus digital) style. I came across it when I had a bad cold, a cold which affected my eyes and made me physically ill just looking at a computer screen. I felt I had reached a limit of my online, screen-staring activities.
(Photos here. Article on how index cards lead to increased creativity here).