A useful record shows what happened, when it happened, which system or activity it covers, and who performed or reviewed the work. Keep enough context to connect it to the control being tested. For example, an access review needs more than a meeting invitation: retain the population reviewed, decisions, reviewer, date, and follow-up. Discuss formats with the auditor because evidence needs depend on the control and procedure. The goal is a clear trail from the stated process to the actual activity. Saving more files is not a substitute for saving records that explain the work.
Related: User access reviews; SOC 2 audit and compliance hub.
Further reading: NIST control-assessment guidance.