What's in the Big Envelope?

I got another package in the mail. Now this one is fairly flat and is a huge white envelope filled with something interesting. It can't be food or treats. It is from http://www.thedogoutdoors.com/ so what on earth is it? It had better not be a dog pack pack for hiking. I don't want to be the beast of burden!

Let me know what you think by commenting. Let's see if Whitley can guess this one!