Assume that you have using magento 1.x version
and assume that you does not want access checkout/cart/
at all time.
For this case you can use Magento Event/observer.
This is case use magento event controller_action_predispatch_checkout_cart_index
and from this event observer redirect to checkout/onepage/
page
<global>
<events>
<controller_action_predispatch_checkout_cart_index>
<observers>
<redirect_to_checkout_from_cart>
<type>singleton</type>
<class>[ModuleNameSpace]_[ModuleName]_Model_Observer</class>
<method>forceToGoCheckoutPage</method>
</redirect_to_checkout_from_cart>
</observers>
</controller_action_predispatch_checkout_cart_index>
</events>
</global>
Observer:
<?php
class ModuleNameSpace]_[ModuleName]_Model_Observer{
public function forceToGoCheckoutPage($observer){
// force redirect to the checkout page
Mage::app()->getFrontController()->getResponse()
->setRedirect(Mage::getUrl('checkout/onepage'))
->sendResponse();
exit();
}
}