almost there with the data structure to send across

fulcrm_shoppingcart.module

@@ -10,6 +10,10 @@ function fulcrm_shoppingcart_permission() {
 function hook_fulcrm_shoppingcart_alter_person_add( $person ) {
 }
 
+function fulcrm_shoppingcart_fulcrm_shoppingcart_alter_person_add( $person ) {
+    return $person;
+}
+
 function hook_fulcrm_shoppingcart_person_add( $person, $redirect_destination ) {
 }
 
@@ -249,6 +253,8 @@ function _fulcrm_shoppingcart_person_add_form_submit_to_data( $form, &$form_stat
     }
 
     $person_data[ 'uuid' ] = fulcrm_uuid_uuid4();
+
+    return $person_data;
 }
 
 function fulcrm_shoppingcart_person_add_form_submit( $form, &$form_state ) {
@@ -283,7 +289,7 @@ function fulcrm_shoppingcart_person_add_guest_form_submit( $form, &$form_state )
             module_invoke_all( 'fulcrm_shoppingcart_person_add', $api_data[ 'data' ], array_key_exists( 'destination', $_GET ) ? $_GET[ 'destination' ] : variable_get( 'fulcrm_shoppingcart_proceed_url', url('<front>') ) );
 
             $form_state[ 'fulcrm_collection' ][ 'person' ] = $person_data;
-            $form_state[ 'fulcrm_collection' ][ 'shoppingcart' ] = $api_data[ 'cart' ];
+            $form_state[ 'fulcrm_collection' ][ 'shoppingcart' ] = $api_data[ 'data' ];
         } else {
             drupal_set_message( t('There was a problem adding your item to the shopping cart.'), 'error' );
         }
@@ -321,7 +327,7 @@ function fulcrm_shoppingcart_person_add( $collection_id, $hmac ) {
     }
 }
 
-function _fulcrm_shoppingcart_buy_eventbookingtype_create_shoppingitem( &$form_state, $person_uuid, $person_name ) {
+function _fulcrm_shoppingcart_buy_eventbookingtype_create_shoppingitem( &$form_state, $cart, $person_uuid, $person_name, $product_id ) {
     $shoppingitem_name = ( $form_state[ 'fulcrm_shoppingcart' ][ 'eventbookingtype' ][ 'event' ][ 'name' ] . "\r\n" .
                            $form_state[ 'fulcrm_shoppingcart' ][ 'eventbookingtype' ][ 'name' ] . ', ' . $person_name . "\r\n" .
                            $form_state[ 'fulcrm_shoppingcart' ][ 'product' ][ 'name' ] );
@@ -417,12 +423,14 @@ function fulcrm_shoppingcart_buy_eventbookingtype_form_submit( $form, &$form_sta
                         $person_name = $form_state[ 'fulcrm_shoppingcart' ][ 'persons' ][ $person_uuid ][ 'name' ];
                 }
 
-                _fulcrm_shoppingcart_buy_eventbookingtype_create_shoppingitem( $form_state, $person_uuid, $person_name );
+                _fulcrm_shoppingcart_buy_eventbookingtype_create_shoppingitem( $form_state, $cart,
+                                                                               $person_uuid, $person_name, $product_id );
             }
         } else {
-            _fulcrm_shoppingcart_buy_eventbookingtype_create_shoppingitem( $form_state,
+            _fulcrm_shoppingcart_buy_eventbookingtype_create_shoppingitem( $form_state, $cart,
                                                                            $form_state[ 'fulcrm_shoppingcart' ][ 'person' ][ 'uuid' ],
-                                                                           $form_state[ 'fulcrm_shoppingcart' ][ 'person' ][ 'name' ] );
+                                                                           $form_state[ 'fulcrm_shoppingcart' ][ 'person' ][ 'name' ],
+                                                                           $product_id );
         }
 
     } else {