diff --git a/src/Contracts/CartConditionable.php b/src/Contracts/CartConditionable.php
new file mode 100644
index 0000000..f477588
--- /dev/null
+++ b/src/Contracts/CartConditionable.php
@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Wearepixel\Cart\Contracts;
+
+use Wearepixel\Cart\CartCondition;
+
+interface CartConditionable
+{
+    public function toCondition(): CartCondition;
+}
diff --git a/src/Exceptions/InvalidCouponException.php b/src/Exceptions/InvalidCouponException.php
new file mode 100644
index 0000000..b0d2dbe
--- /dev/null
+++ b/src/Exceptions/InvalidCouponException.php
@@ -0,0 +1,7 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Wearepixel\Cart\Exceptions;
+
+class InvalidCouponException extends \Exception {}
diff --git a/src/Exceptions/InvalidShippingRateException.php b/src/Exceptions/InvalidShippingRateException.php
new file mode 100644
index 0000000..ab8ca94
--- /dev/null
+++ b/src/Exceptions/InvalidShippingRateException.php
@@ -0,0 +1,7 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Wearepixel\Cart\Exceptions;
+
+class InvalidShippingRateException extends \Exception {}
diff --git a/src/Exceptions/InvalidTaxRuleException.php b/src/Exceptions/InvalidTaxRuleException.php
new file mode 100644
index 0000000..95448d6
--- /dev/null
+++ b/src/Exceptions/InvalidTaxRuleException.php
@@ -0,0 +1,7 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Wearepixel\Cart\Exceptions;
+
+class InvalidTaxRuleException extends \Exception {}