There are a few add-ons you could use to create shipping charges for a domestic and/or international order.
Grouped Products: Good for grouping one product to another. Note: If used in conjunction with USA Only or Countries to Include, this is a great solution if you have digital AND physical products.
Forced Products: Good for forcing 1 or more products into the cart (such as a domestic shipping product). Note: If used in conjunction with USA Only or Countries to Include, this will force the product for everyone (does not delineate between foreign or domestic).
International Shipping: Allows to group products for domestic or international shipping based on their shipping country (does not work with Cart Mode).
International FORCED Products: Forces specific products into the cart based on shipping country (works with Cart Mode).