I now have a trusted system that is easy to use and allows me the freedom to carry one thing.
My iPhone (a 5, but I was with the same thin with a 4) has a great Mac-based software called "Things" which has an iPhone, iPad, and Mac client. Things syncs in the iCloud system and makes sure all of these items are consistent on every platform.
Unfortunately, there are type when I cannot pull my iPhone out and enter a quick task into the program (when I face-to-face with a client for instance). Go I have used some 3M removable adhesive strips on the back of the phone, and "taped" a Flipnote notepadon the back - http://wellspringgift.shptron.com/c/flip-notes - when the Flipnote is aligned with bottom of the phone, it does not get in the way of the camera, etc. (although I'm sure steve jobs would not approve).
When I get back to me home office I drop any paper notes I've made into my physical in box and add them to Things
My problem is that this would be foolproof if I could remember what I had already entered and what I had not. So I could fill up a pad that has the same reminder that I already entered yesterday or that I entered earlier that day on the note pad.
I seems to me that if I could come up with a consistent way of alphabetized the tasks, I could use small cards instead of the notepad entries - so i could as least try to catch duplicates.
I know one of the benefits of GTD is to get things out of your head, but instead that has translated to having all these item in my head to juggle to making sure I have all these items into GTD.
Surely I can't be the only one who has encountered this problem.