Drupal Commerce: Can I have product list and checkout in the same page?
Try Commerce Express Checkout


  The Express Checkout button redirects to the Checkout page directly,
  without going to the Cart first, It also removes the Review page and
  adds the Payment checkout pane to the Checkout page, so the whole
  checkout process is done on one page.




Ckeck 


http://www.drupalcommerce.org/discussions/952/all-checkout-steps-one-page 
http://atendesigngroup.com/blog/express-checkout-drupal-commerce