I use a Google sheet to track mine. Columns are: date, activity, hours, and notes (what I learned, specific surgeries I watched, tasks I completed, etc)
I have a separate spreadsheet for both shadowing and volunteering. For shadowing, I color code based on the physician (highlight all dates blue for orthopedics and yellow for pediatrics, for example). I just like having a visual representation and I really like notes to jog my memory later when reflecting upon those experiences.
I am the spreadsheet queen though so it might be too much for most people to want to do, but I really enjoy it!