Product incorporating existing product.

[vintagejewelers]

I'm new to shopify and am entering products to build out my inventory for online sales, and in store sales. I have a Jewelry store and we have many products and services that we offer. I'm having difficulty figuring out how to create a specific service for in store sales. We sell watch batteries, and I've entered all the different types of batteries as variants for taxable sales. Now, that they are entered as products, I'll be able to automatically re-order them when I get low. I also offer two different price, watch battery installations, which is non taxable, but incorporates the taxable watch battery. How do I create a product (service) which incorporates a pre-existing product?