I agree with Brian - the list changes constantly based on what's needed for a given trip.

However, in the spirit of the OP's question (and because it beats working), here's the big stuff that lives in my pack most of the time (Conditions: 3-season in the Ohio River valley):

Gregory Savant 48 or 58 pack, depending on length of trip and cold weather clothing taken.

MSR Carbon Reflex 1 tent; I also take either the footprint or the "mud flap" (vestibule-only footprint) that get used more often as a ground cloth to sit on at lunch, breaks, or around camp. The full footprint also allows me to make a fly-first pitch when it's raining, then attach the inner tent where it's dry. The tent lives in two small stuff sacks (one for the inner, one for the fly), which is more flexible for packing and keeps a dry inner separated from a wet fly.

MSR Hyperflow filter, Nalgene 1-liter bottle (because it has measuring marks and because I like it), and an MSR Dromlite 2L or 4L bag, depending on how much water I might have to carry - inflated with air, it makes a great pillow.

MSR Micro Rocket, Titan kettle, and Titan spoon - entirely adequate for boiling water once a day (twice, if I also want morning tea.) Nice, compact kitchen that stores in the same bag as the food.

Thermarest NeoAir XTherm (48 or 66 inch length, depending on season) - very warm, very comfortable, incredibly light and compact. With the 48 inch, I store my pack under my lower legs; in cold weather, I store it crosswise at the foot of my tent, just beyond my feet which are on the 66 inch pad. I used to carry the chair kit religiously, but find that I'm leaving it behind more often, taking a NeoAir or Z-lite sit pad instead, because it's easier, lighter, and works well with the ground cloth.

Western Mountaineering sleeping bag - Alpinlite, Megalite or Mitylite, depending on forecast temperatures. ("You can have my WM bag when you pry if from my cold, de...wait a minute, I'm never cold in it.") Also WM Flash jacket, pants, vest and/or booties, depending on temperatures. (The bags are roomy enough that I can wear the clothes inside it, which gives me a safety margin when it goes colder than the forecast.)

An Outdoor Research Foray rain jacket and pants, which double as long pants or windbreaker as needed.

A spare pair of wool hiking socks - last, but a long way from least. There's no greater pleasure than changing into clean, dry socks just before slipping into the sleeping bag. (Well, almost no greater pleasure.)

That's about it - nuts, now I gotta go back to work. (It's called work because all the other 4-letter words were taken.)