In short, GTD only tracks my actions; not the things I need to perform those actions.
GTD helps me track every single open loop that I have outstanding via the Projects Lists. GTD helps me track the progress on every single Project (Moving Piece) via the next action list. The next action list is organized by context (physical/logical) so I can move my projects forward whenever I am in that context.
The problem I am having is tracking the project support materials and bringing them w/ me whenever I travel to another context.
For example, I am at home and have to go to the bank. I realize I will be standing in line for 15 minutes. I am confident I will have something to do b/c I have organized my NAs by context. I get to the bank, look at my @Anywhere list and see "Read GTD", only I did not bring the book. I read down the list and see "Work on Club Arcadia", only I did not bring the Arcadia folder (filed in my filing cabinet) or any support materials.
GTD tells me what I can do at any given moment, but it does not tell me what I need to accomplish that task. So I need to retain in my head all the information on what support materials are needed for each task, so as I scan down the NA list I can take these materials w/ me as I travel.
What methods have others used to overcome this limitation?