Adding Product'S'

Hi all, i had a new requirement,where i need to add more than one product to cart at the ‘Add to Cart’ section, i am able to display the sub products to the product as checkboxes if a user selects 2 subproducts and he clicks on AddtoCart, he will be having three products, as the Onclick Function for AddToCart is assigned at page load i am unable to remove or add more functionality to it. Please show me the solutions.
Thanks