diff --git a/README.md b/README.md
index 2ce637e..3bdd190 100644
--- a/README.md
+++ b/README.md
@@ -50,10 +50,14 @@ After creating your implementation of this interface, you must supply it to your
 ```php
 interface cartStorageInterface
 {
-	public function init( cart $cart ) : cartStorageInterface;
-	public function saveCartItem( cartItem $item ) : cartStorageInterface;
-	public function saveCartData( cartData $data ) : cartStorageInterface;
 	public function loadCart( cart $cart ) : cartStorageInterface;
+	public function emptyCart( cart $cart ) : cartStorageInterface;
+
+	public function saveItems( array $items ) : cartStorageInterface;
+	public function saveData( array $data ) : cartStorageInterface;
+
+	// used to clean up after all storage is complete
+	public function finalize( cart $cart ) : cartStorageInterface;
 }
 ```
 
diff --git a/src/cart.php b/src/cart.php
index 07badef..035a4fd 100644
--- a/src/cart.php
+++ b/src/cart.php
@@ -218,10 +218,10 @@ public function save()
 		$this->storageHandler->saveItems( $this->items );
 		$this->storageHandler->saveData( $this->data );
 
-		$this->storageHandler->finalize();
+		$this->storageHandler->finalize( $this );
 	}
 	//------------------------------------------------------------------------
-	public function addData( cartData $data ) : self
+	public function addData( iCartData $data ) : self
 	{
 		$this->data[$data->getType()]  = $data;	
 		
diff --git a/src/cartData.php b/src/cartData.php
index 11abc9f..24dc6ef 100644
--- a/src/cartData.php
+++ b/src/cartData.php
@@ -1,7 +1,7 @@
 <?php namespace treehousetim\shopCart;
-use \stdClass, \Exception, \ReflectionClass;
+use \stdClass, \Exception;
 
-abstract class cartData implements jsonSerializable
+abstract class cartData implements jsonSerializable, iCartData
 {
 	protected $data;
 	protected $type;
diff --git a/src/cartStorageSession.php b/src/cartStorageSession.php
index 928a6e4..eb6ed28 100644
--- a/src/cartStorageSession.php
+++ b/src/cartStorageSession.php
@@ -26,7 +26,7 @@ public function saveItems( array $items )
 
 		$_SESSION['cart_items'] = [];
 
-		foreach( $this->items as $item )
+		foreach( $items as $item )
 		{
 			$_SESSION['cart_items'][] = ['id' => $item->getProduct()->getId(), 'qty' => $item->getQty()];
 		}
@@ -51,6 +51,8 @@ public function saveData( array $data )
 	public function finalize( cart $cart ) : cartStorageInterface
 	{
 		// do nothing
+
+		return $this;
 	}
 	//------------------------------------------------------------------------
 	public function loadCart( cart $cart ) : cartStorageInterface
diff --git a/src/iCartData.php b/src/iCartData.php
new file mode 100644
index 0000000..7251634
--- /dev/null
+++ b/src/iCartData.php
@@ -0,0 +1,11 @@
+<?php namespace treehousetim\shopCart;
+
+interface iCartData
+{
+	public function jsonSerialize();
+	public function getForStorage();
+	public function setData( $data ) : iCartData;
+	public function getData();
+	public function setType( string $type ) : iCartData;
+	public function getType();
+}
\ No newline at end of file