Display product add on text onto the product image
Allow users to see a preview of the product with the customized text they enter into the text boxes.
For example if they want an item engraved with various names they would currently enter it into the product add on text boxes. Customers want to see where each name would go and get an idea of what it looks like. Amazon already provide similar functionality and honestly its what customers EXPECT in this day and age.
I can provide various websites that currently do it and its a much better user experience.