First of all, congratulations on med school.
I think some of the most valuable GTD principles for med school relate to mapping energy to next actions.
It will be difficult to plan your med school study and survival techniques before you get a feel for the coursework. But, the amount of memorization surprises every med student. Developing an approach to track the scope of material for each test, and the status of learned (= memorized) work should be helpful. Having lists of NAs that will help move things forward even when energy levels hit a low, will help.
Caveat: A few things may have changed since my med school days in the 1800s.