Auto Add products to Deal/Opportunity

Auto Add products to Deal/Opportunity

Hi All

Looking for some help. 

I am looking to auto add products to a deal based on additional fields within the system. 

E.g a Picklist box that says transfer or register, depending on the outcome will associate the relevant product to the deal. 

I have a series of picklists that a user selects. Adding the products to the deal also will be duplicating work. 

cant see a way of doing this with workflow.