In a similar vein to Thomas Thwaite's 'How I built a toaster from scratch' and AJ Jacobs' Thanking a thousand people for my morning coffee', this video demonstrates just how much we gain from specialisation by looking at just some of the steps taken to make a sandwich from scratch. There is a short overview video here, or individual videos on each step of the process here, giving you the option of setting different students to look at different stages of the production process.
There is also a response video from Wendover Productions, looking at Why Chicken Sandwiches Don't Cost $1500. This looks at specialisation, economies of scale and diseconomies of scale by focussing just on the salt that went into the sandwich. I particularlly like the explanation about why it makes sense to have just 1 salt factory, but multiple Coca-cola factories. There are quite a lot of numbers in the video but you don't really need them to get the gist.