KamGraphica

// check for clear-cart get param to clear the cart, append ?clear-cart to any site url to trigger this
add_action( 'init', 'woocommerce_clear_cart_url' );
function woocommerce_clear_cart_url() {
	if ( isset( $_GET['clear-cart'] ) ) {
		global $woocommerce;
		$woocommerce->cart->empty_cart();
	}
}

KamGraphica

  if (typeof Shopify === 'undefined') var Shopify = {};
  Shopify.cart = {{ cart | json }};
  Shopify.toAdd = 378589397;
  var surchargeInCart = false;
  var total = 2507; // total in cents.
  for (var i=0; i<Shopify.cart.items.length; i++) {
    if (Shopify.cart.items[i].id === Shopify.toAdd) {
      surchargeInCart = true;
      total -= Shopify.cart.items[i].line_price;