well, I think many of these solutions are not working or too complicated. I just added to customer/main/cart.tpl the following code:
Code:
<TD align="right"><TABLE border="0" cellspacing="0" cellpadding="0" onclick="javascript: self.location='home.php'" style="cursor: pointer;" valign="middle">
<TR><TD>[img]/cart/skin1/images/but1.gif[/img]</TD>
<TD class="Button" valign="middle" nowrap><FONT class="Button">Continue shopping</FONT></TD>
<TD>[img]/cart/skin1/images/but2.gif[/img]</TD></TR>
</TABLE>
right above the code
Code:
<TD align="right">
{include file="buttons/button.tpl" button_title=$lng.lbl_checkout style="button" href="cart.php?mode=checkout"}
</TD>
it is in around line 99 in my file (version 4.0.11).
This is the original xcart code from the invoice page, there is already a Continue Shopping button.
Andy