Before creating your bundle, ensure that you have made an informed decision on whether to create a Single SKU Bundle or a Multiple SKU Bundle, because you will not be able to change this once the bundle has been created.
It's also important to make sure that thedetails for each productyou wish to add to your bundle are set up correctly by heading to Admin > Products.
If your products have variants, ensure that these have already been added into place before you create your bundle - this includes assigning variant images, the weight, and the shipping cost.
It's essential that the products you add to your bundle do not use a third-party service to house their variants (e.g. Printful), as Bundle Builder will not function without access to the correct information from Products within your Shopify admin.