Before a long tour I really have my bike gone over for a complete inspection. Change out the obvious unless they are in great shape. Some friends would not ride with STI index shifters? Too great a chance for a break down, since they are not simple systems? I have a difficult time with that one. I like my STI.
Obvious parts. A spare tire, a second chain. Mabye a spare hanger since they are quite vunerable. And yes, some spare cables. Might be helpful to know how to install your spare parts?