I'm pretty new to touring. What should I be checking before going on a three week tour?

I've always been a little mystified about tires. Knowing they're totally worn out doesn't seem too hard. Knowing that they're nearly worn out is harder. How do I tell? I'm running a set of michelin Comfort Contacts that have a few thousand miles on them. I can't tell that they're significantly worn. But rather than just look for signals and not know exactly what I'm looking for I'd like some kind of measurement or specific method to be following.

This bike was brand new in November 2012 so I don't much expect a lot of mechanical wear. But it would be nice to be in the habit of knowing what to look for.

I know myself and given a long list of things to check, I won't do it. I don't love to tinker. I love to ride. But a short list of the most critical things is something I'm looking for. I want relatively easy things to check that might otherwise be missed and especially things that might be particularly difficult to deal with while on tour.

I'm going all over the bike tightening stuff, especially hardware that holds my racks on (Surly Nice Rack). Where would I find some replacement allen bolts that hold my racks & water bottle cages etc? It would be nice to have spares. I don't know if my bolts are different depths. Do I need to remove them all to find out?

How fast do disc brake pads wear out? How do I know if they're near the wear limit? (Avid BB7)