I Would do Unspeakable, Sordid Things for These

Travel checklist musts:
-Passport
-Copy of passport
-Currency, local and American
-Combo lock
-Flipflops
-A towel (Hitchhiker's Guide to the Galaxy fans and guests of disgusting hostels, unite!)
-Quality headphones

I am not negotiable about any of the above. Beyond that, I usually like to bring Honey Nut Cheerios and a list of addresses.

http://www.gradolabs.com/frameset_main.htm
http://www.buy.com/retail/product.asp?sku=210401797&listingid=41901817&dcaid=17902

One day, I hope to be as good at what I do as these guys are at their purpose.