Store any type of document or piece of information against a user profile, by creating custom fields. This could range from documents/files like personal liability insurance to first aid certificates; and extra information like membership numbers, or alternative contact details. 

When setting a reminder notification, you can choose for the reminders to go to a certain role or person, or the user themselves. The enable reminders for the users themselves, use the "Notify User" toggle after setting the reminder time.