List at Checkout by Catagory?

Not sure how to label this. I need to offer certain customers certain products at checkout. That being said, is it possible to assign blocks of products at checkout by catagory or even products? So, if somebody has a certain product in their cart, the cart would recommend designated products at checkout.

Not sure if this would work but have you tried putting a “Customers also bought” block on your checkout page? You could assign usergroups to your products to control whether they are displayed in the block (and in the storefront).