You wouldn't necessarily need an individual receipt for every
service; an account statement showing payment for all services during the year
from a particular provider is acceptable. As are printouts from your
local pharmacy for prescription amounts paid throughout the year.
An insurance statement -- which in itself probably wouldn't prove payment, merely the amount you were "responsible" for -- coupled with a credit card statement or cancelled check, would also work.
Should the IRS ask for supporting documentation, the key is to have documentation proving amounts actually paid, rather than invoices or bills.
