This is Bart's luggage arrangement. It was actually a very clever set-up - it carried the weight lower than Shaun's, and did not require a special luggage rack either.

The black Adidas back-pack had Bart's clothes, while the blue bag had all of his Spares, tools, etc. as well as a 10 litre (2.7 US Gallon) fuel container. The blue bag is actually "wearing" the back-pack (ie, the Adidas bag's shoulder straps go around the blue bag.) This meant the entire arrangement acted like one piece, which made loading (and removal) quick and easy.