Add a reminder function to the Booking Overview page

Or attached to the Notes field?  Triggers and Alerts are for all properties and not customizable for one booking only.  Good for "send welcome letter with directions 3 days prior to arrival" but not so good for one particular booking that you need to buy groceries or flowers or whatever for (items out of the norm), or even just a note to self to do something linked to that one particular booking.  Would be very helpful please. Thank you.