I think it's helpful to keep an evolving, updated CV with a short description of each activity (~1-2 sentences). Having the list in CV/resume form makes it easy to work with when you need to hand it over to someone in the future or convert it into an application (say, AMCAS!). I keep a "cumulative" CV and then, when I am applying for something, I save an extra copy of this, edit it down (deleting information to make it more specific to whatever I am applying for), then save as a separate, more specific resume.
If you do something so minute that you'll forget you even did it a year, then it probably isn't too important. Keep track of awards-you'd be surprised how you'll forget these quickly (speaking from experience...)