Specific order confirmation based on collection product bought

[Foyboy]

Hello, 

I manage an online store for my sisters business which currently only offers collection from a bakery studio on specific days based on the product range on sale such as Valentine's Day, Mothers Day etc. 

Currently I am manipulating the standard order confirmation for the specific range on sale as we only do one at a time. We do want to have multiple ranges on sale but have a very specific collection date defined on the order confirmation. 

What is the best way to do this, is it either shipping zones/rates or html code in the confirmation email? 

Thanks!

Allan