When you do the timing belt you should do:
The belt, water pump, drive belts, plugs, thermostat and valve cover gasket set. Since you have take off stuff and open the cooling system, it just makes sense to that stuff together. Adjust the valves when the valve cover is off- I've only done it once, but that's because I usually screw up this relatively easy process! The seals and tensioner should be done, but that's your call (I have 349,000 miles on my tensioner). The cap, rotor, PCV, air filter and fuel filter should be done when they are needed.

Edit: I get most of my parts from Autohaus AZ, but for some stuff (suspension especially, I get OEM from Majestic). Most of the tune up stuff and high wear items I just get from Autozone- brakes, CV's etc. Drive belts are one thing because it's easier to return when they give you the wrong sizes!!)