There seems to be some confusion as to how to bundle your items to sell on Amazon. A good place to start is to read Amazon’s guidelines posted right here.
Your bundle should consist of highly compatible products. A great way to get ideas is to look at what Amazon says “this customer also purchased”. You will need a UPC code when creating your unique listing. It should be placed in the category with the main, usually most expensive item. Don’t try and list items in a category where you are not approved to sell as that is against Terms of Service.
Here is an entire course on the subject if you’re looking for some help.