There are a lot of commonalities with previous posts on this list, but it is easier for me to be inclusive.
Patch kit with extra small size patches. These are the ones I use the most.
Tire levers.
Park spoke wrench.
Kevlar Spoke.
Park CT-5 chain tool.
Sram Quick Link.
4 oz chain lube.
12 ml. hypodermic syringe filled with Tri-Flow oil. For derailleurs etc.
Multi-tool. Make sure the hex that fits your shift lever clamp bolt (STI) is long enough to reach. Minor crashes often move shift levers rather than breaking them if tightened correctly. I found out the other day that the one my wife carries does not! Also make sure there is a hex that is small enough to fit your brake centering bolts
SS coupling wrench Wife's bike has SS couplings. Wrench also has a pedal wrench which is necessary if you are shipping/packing bike at end of tour.
Park 8/10 mm open end wrench, CBW-1 Small and fits SKS fender strut nuts.
Small assortment of spare bolts/nuts Including a cleat bolt.
Spare cleat if using Look (nylon) type cleats I've broken three in the last 3 tours. Switching to SPD's
2 or 3 one inch pieces of 3/32 heat shrink wire insulation. It make a great cable cap if you loose one or need to replaces a cable.
1 spare derailleur and brake cable. Never used them yet, but there were a couple of times I should have.
2 bar end plugs. It seems like I lose at least 1 per trip.
Small 3x5" sponge. A soft drink cup or a plastic bottle with the top cut off makes a good disposable bucket. Dish soap works well for keeping bike clean. Napkins and paper towels scrounged along the way are great for wiping chains.
1 or 2 pairs of nitrile or latex gloves. good when messing with your chain. Can also be picked up along the way at Subway sandwiches, etc.--Just ask and they will usually give you a pair of vinyl food handlers gloves.
All this fits in a 5x8 plastic box. In addition I usually carry a folding spare tire.
This has been used a couple of times, and I was glad I had it. Sometimes, I'll also carry a Leatherman type multi-tool. The file, pliers and wire cutters have come in handy. This is for 2 bikes and multi-month tours. For shorter tours I don't usually carry spare cables. On longer tours I also throw a pair of nail clippers in my tool box.