FoxKit: Upsell & Bundles App

This app is literally an all in one powerhouse to add to your shopify store! It has all the key features you need to upsell, crosssell, make subscribe pop-ups, give discounts based on products added to cart, and so much more. And not to mention the fantastic support, they reply super quick and give you easy to understand help (PS, if you get Linh helping you, just know your in good hands).