Until now, Google Checkout Buy Now buttons, only allow to purchase one item at a time from your website. But now, the new Google Checkout shopping cart allows your buyers to add multiple items, change item quantities, and remove items -- all without leaving your site.
To get started: visit the Google Checkout shopping cart page located under the Tools tab in the Google Checkout Merchant Center. Enter your product information, price, and image location. An HTML snippet will be generated for you to insert on your product web pages. Test the button, by clicking it, if a shopping cart should appear in the upper right hand of your browser window, you're good to go.