The following tutorial will guide you through adding content to the receipt that is only displayed when the customer purchases a specific item. First hover over the StoreFronts menu on the left hand navigation and select the StoreFront you're working with as shown below.
Next click on "Templates" and then click on "Checkout"
Scroll down until you reach "templates/system/checkout/receipt.vm" as shown below.
Now scroll down in the file to around line 213 where you will find "form.htmlOrder". We are going to place our content just above that. An example snippet of code is:
## Start Conditional if item earthtone_mug is purchased
Special custom content goes here.
## End Conditional if item earthtone_mug is purchased
After placing the code into the page, make sure to click save. The steps are shown below.