You can add images to your bundle by editing your design settings.
Go into the Bundle Builder app through Apps > Bundle Builder.
Go to Bundles, and the select the bundle you wish to edit.
Select Design, and scroll to Imagery.
Your product image is displayed in both the checkout and in email notifications.
To add this, go to Imagery > Product image, and select Upload.
To add an image for the header of the bundle page, go to Header image and select Upload.
Under Header image width, you have the option of setting your header image to:
Default - where your image sits in the center.
Full-width - where your image stretches to align with the content on the page.
Match page content - where your image stretches to fit edge-to-edge of the browser window.