Okay,
I’m flying blind here, I only have the demo version of RCP.
Sound like you are trying to build the menu manually and not use the RW menu option?
I just tried this and it seems to work with the Demo store.
I copied this into the HTML contents on a menu item:
<i class="uk-icon-shopping-basket uk-margin-right"></i><span class="rc-extras-cart-total"><?php echo $rc->extras->cartTotalLocalized; ?></span></span>
Then with that menu item selected in the stacks setting I set the link to the store(in my case it was the demo store since I don’t have RCP live).
Don’t know if it will work with a live site or not. I did notice you need an RCP product or Cart or the shopping cart doesn’t show up. You can set it to be hidden but the icon doesn’t seem to load any other way.