When you're packing for a 2-3 day Alpine climb to a mountain like Rainier or Grand Teton, it's easy to say, "I'd better pack this jacket, just in case." But the consequences are usually the same: the heavy load slows you down.
Review your gear. Replace the mechanical plug with Hex and put on a lighter weight wire-gate carabiner. If possible, talk to friends who have climbed the route to determine what equipment to bring.
Get rid of everything you don't need. Do you really need an extra pair of socks? A toothbrush? Headlamp backup battery? Talk to your partner about sharing lipstick, knives, first-aid kits, etc. For items in doubt, clear them out.
Use lighter ice axes and crampons. Ice axes weigh between 10 and 30 ounces (285-850 grams), bring the lightest one, but it should be able to make skid brakes, cut steps, etc. Similarly, a pair of walking crampons weigh about a pound (454 grams) less than a pair of climbing crampons and are more comfortable to walk on.
Simplify your cookware. Bring only one pot (aluminum or titanium) and leave the dishes at home. You can bring a lighter gas stove instead of a heavier liquid fuel stove. Eat only one hot meal a day and make it easy to prepare. A mix of instant potatoes, soup and a few spoonfuls of butter is simple and provides plenty of energy.
Put on all your clothes and go to bed. This will allow you to pack a lighter sleeping bag and avoid cluttering up your clothes in the morning. Equal weight of high quality down produces the best insulation. But remember that down becomes useless when wet. For longer wet weather trips, a synthetic-filled sleeping bag is a better option. Not paying too much attention to the sleeping bag you choose, then bring a camping bag for a mixed technical route, two camping bags also weigh less than a tent, and use the flat rock face as a camping platform. With a single tent on your back, it is usually easier to find a good camp site in the snow, with all the protection you need to save your life in the event of the wrath of God.
Weigh your backpack and sleeping mat. Start with your backpack: If you have an aluminum frame and a plastic back pad, replace it with a folded foam pad. Your backpack will be more in tune as you move. During the summer on the rocky route, you can pull out the foam pad at the campsite and sleep on it. Of course you'll be less comfortable than a two-pound inflatable cushion, but the weight saved will pay off when you climb. If you have to sleep in the snow before summit day, or if you don't want to put away your fancy gear, bring a half-length inflatable cushion. When camping, put your legs on an empty backpack and rope and lie or sit on an inflatable cushion.