Well, in filemaker, you don't copy data to layouts, you copy data to tables and then only if you need to. I don't see a reason to do that here.
If you limit your found set to just one donor's records--all you'd need for a receipt, the summary field would then report the total donations just for that one donor.
The other option is to add sub summary part with the "page break after every occurrence" option specified so that you can print out all the receipts for all the donors in one batch, but have each donor's receipt start on a new page.
There is a way to access the subtotal inside a sub summary part with the getsummary function, but I don't see the need for that here.