cd YOUR-APP-FOLDER
git submodule add git://github.com/burzum/Cart.git Plugin/Cart
git submodule add git://github.com/cakedc/search.git Plugin/Search
git submodule update --init
If you do not want to add it as submodule just clone it instead of doing submodule add
git clone git://github.com/burzum/Cart.git
If you use another user model class in your application other than User you'll need to configure the plugin to use that model:
Configure::write('Cart.models.User', 'AppUser');
Don't forget to load the plugin with boostrap true.
CakePlugin::load('Cart', array(
'bootstrap' => true,
));