Making sure I'm warm enough--I get cold easily, especially at night. I tried a 32* (0*C) sleeping bag with all my extra clothing; I was shivering by the time the thermometer reached 32*! I also don't do well with quilts (cold drafts down my neck when I toss and turn). I'm much better off with my Western Mountaineering Ultralite.
A really plush thick, well-insulated sleeping pad--with my old bones and slightly arthritic joints, my choice is between a really thick insulated air pad or spending the night literally screaming in pain! My 3.5" thick insulated pad from the late lamented KookaBay is 13 oz., so it's really not all that heavy. I tried the NeoAir and couldn't get comfortable on it.
A canister stove (Primus Micron Ti), for its convenience. For long trips (over 7 days), the weight difference between alcohol and canister is minimal. For 2-3 day trips, I really should take my alcohol stove, but I always end up grabbing the canister stove instead. At least that lets me use up my collection of partially full canisters.
A personal locator beacon--I call this psychological weight saving, because it keeps my family and friends off my back!
As a result, my base weight for 3 seasons (Cascades and Rockies) is either 10.8 or 12.2 pounds (4.9 or 5.5 kg). The higher weight includes camera (for some reason, missing from nearly all the gear lists I've seen) and fishing gear. (The fishing gear includes a frying pan just in case I catch something, ha ha.)