It looks good, but pckry
isn't currently defined in your script. Instead of attaching Packery to the jQuery object, you can instantiate a new instance of Packery and define it as pckry (or whatever you want) like:
var pckry = new Packery($container[0], {
itemSelector: '.item',
gutter: 10
});
Note the [0]
after your jQuery object to reference the original DOM object.