Premium subscribers have two additional templates for thanking donors and guests (including details of their support) via email.
To View/Edit Templates:
Go to: Admin > Site Settings > Communications > Email Templates > Thank You Templates:
To Create Custom Template:
The above merge tags will display "No Donated Items" or " No Purchases or Cash Donations" if user did not donate/purchase. If you are intent on sending a custom template containing both donor and guest merge tags, be sure to send test emails to users with only purchases or only donations to make sure the placeholder message(s) displays coherently with your text/formatting.