I have always kept physical to-do lists and notes. On scrap pieces of paper, sticky notes, envelopes, etc. I get great satisfaction in making a list of things to do, and then methodically crossing off all the items as I complete them. I am also always thinking of business-related things that I know I would lose if I didn't jot those ideas down immediately.
I formalized (or centralized) my to-do and note scribbling when I discovered Field Notes a few years ago. Such well designed little booklets that fit easily into a pocket and have great brand feel are right up my alley. Now you'll almost never find me without a small, beat-up Field Note booklet (with graph ruled pages!) and a pen.
I have digital to-do lists and note apps I use on my iPad mini and iPhone as well, most notably OmniFocus and Evernote, with some light usage of others here and there like Wunderlist, Apple's Reminders, or 53's Paper. The digital apps are amazing because they can remind you to do things at a certain time or a certain place, they sync everywhere, and text can be searchable. Those things are all fantastic and they have their place, but none of that can replace a physical object that comes with me and that I can experience in a tactile way.
I thought that one day the digital apps would replace the paper, but I'm not sure that's ever going to happen. Much like with digital books versus a good ol' trade paperback, the digital to-do lists and note apps are "superior" in many ways, but nothing can take the place of the original. I tried making it a more tactile experience by buying various iPad-compatible pens and pencils (including 53's Pencil) but I find that as cool as these things are, I never use them. They all end up in a drawer. I just can't envision grabbing my 53 Pencil, turning on my iPad, opening up Paper app, and then sketching out some random idea I have on how to better structure a client webpage. I could have been done with it on paper before I even put my finger on "slide to unlock."
There, done. Now I can pop the cap off my pen, flip to page 7 and cross off "[ ] write blog post."