Add Custom Line item API or Method Drupal Commerce I have some products in a Drupal Website using Drupal Commerce. Those products are listed via a custom modules to the front end. If the user clicks on any of the products then it goes to the product display page. There I have 2 checkbox and the Add to Cart Button. Such as 


Gift Packaging ($10.99)
Custom Messages ($4.99)
These are 2 checkboxes coming from a drupal form created on my custom module. 
I want to add these as line items to the Selected Product. Such as, 


If user choses Product A and Gift Packaging then,
Product A ($10.00)
Gift Packaging ($10.99)
Total : $20.99


So how can I add the chosen line item to that product once the user clicks on the Add to Cart Button. I have a function that is fired once the button is clicked. The function is "my_module_add_to_cart()".
How can I show the updated Price as $20.99 to the /cart page table?
Why not use Commerce Product Options which provides this functionality out of the box, directly in the default Add to Cart form?

To adjust the price based on the chosen options, you can use the Commerce Pricing module, which comes as part of the Commerce project. It basically provides a number of rules conditions and actions which allow you to adjust the price of a line item and e.g. add a fixed amount or multiply it by a certain value.