Why you would not want "go to checkout" on the shopping cart page is an utter mystery to me - especially since the whole purpose of an eCommerce site is to coerce customers into doing just that!
I have a solution for the sidebox and though it breaks a few rules (ie: it hard-codes into the PHP) it does the job.
FTP a COPY of the following file to your hard drive:
includes/templates/template_default/sideboxes/tpl_shopping_cart.php
Open it for editing using a PLAIN TEXT EDITOR, such as EMERALD EDITOR
Right at the bottom, find the following (last two lines)
$content .= '</div>';
?>
Make the following edit
$content .= '</div>';
$content .= '<div id="checkoutButton"><center><a href="index.php?main_page=shopping_cart"><img src="includes/templates/template_default/buttons/english/button_edit_cart.gif" alt="Edit Cart" title=" Edit Cart " width="61" height="20" /></a> <a href="index.php?main_page=checkout_shipping"><img src="includes/templates/template_default/buttons/english/button_checkout_sm.gif" alt="Checkout" title=" Checkout " width="61" height="20" /></a></div>';
?>
As you can see, this also requires the creation of two small additional buttons that need to go into:
includes/templates/template_default/buttons/english
called:-
button_edit_cart.gif
button_checkout_sm.gif
In my example, the dimensions of these buttons is 61px X 20px . You decide how wide they need to be - a decision influenced by your side-column width.
NOTE: If you don't include the button images, you will just get the ALT text as the link
When you have made the edit, SAVE the file on your hard drive, then FTP it to your CUSTOM TEMPLATE folder for sideboxes:
includes/templates/YOUR_CUSTOM_TEMPLATE/sideboxes/
If there is no folder for sideboxes in your custom template, create one...
As I say, this method is bad protocol as it hard codes the php. Somewhere I do have the correct PHP version, but I haven't time to look for it right now.
You will also see I have given it a style ID
div id="checkoutButton"
.. allowing you to add some styles if needed.