only thing that comes to mind is the "text option", if it's something product-related (like Text that's supposed to go on that T-Shirt that you sell etc.)
That will not do the job. What I mean is when you order an item (with pick-up in store option) but then in a note you will introduce a third person to go to store for pick up or ...
where would that note go to? An Email? Or should that be some customer-related data to be viewed in the Admin area? Like "Customer Info", "Customer Adresses", and now "Customer's representative" (Which would probably require some changes in the Database...)