'strict mode'
So I was at the HTML5 meetup about web accessibility in Montreal - that took place at shopify's place. I saw you guys were looking for an intern, so I started to hack this. It took me around an hour and I was listening to conversation.
It's not flawless - I would have used Promise and/or ECMA6 if I had the time, but it does the job. Keep in mind that I was really hungry - I didn't even took the time to have some pizza you proposed. The code deamon got me.
There's a trick in your challenge - you said to buy everything in the store, but in which color? That's why I added a feature - you can now set your prefered color in the PREFERED_COLORS variable and he will take that into account. The order is important : if you prefer light blue over dark orange (if that exists) and that both are proposed in the shop, he'll choose light blue. If there's none of your favorite colors, he'll just take the first variant.