Use the Manufacturing module and define a Bill of Materials (BoM) for the Product that is sold in a box. Define the BoM with a type of "Kit". Set the Product sold in boxes as "Can be sold" and products x, y, and z as "Can be purchased". You will then be able to sell a box and the system will automatically translate the box into it's components and keep a track of them. You will also be able to define reordering rules for products x, y and z.

Thanks Craig, Ill try this.

I'm pretty new to Odoo myself, but I'm pretty certain this can be done and without customization. 

Perhaps you can set up packaging (this is a setting available to community version). I have not used this but I believe it allows you to add multiple products together into a package that can be sold. Here is a link to information regarding packaging. Also, a simple google search will bring up videos related to the subject.

https://www.odoo.com/documentation/user/14.0/inventory/management/products/usage.html#packaging

Another option might be to use the manufacturing module. In this instance you would create a bill of materials (the lowest level parts) that make up the finished good (what you sell).