These lightweight backpacking tips and techniques are options or ideas, not recommendations. I tend towards the extreme side of ultralight backpacking, and if you don't know yourself or your skills, some of these techniques will get you into trouble.
A good example of this is the "natural mattress" that allows you to leave your sleeping bag behind. With this technique, I've slept with no pad, and only a five-ounce sleeping bag liner, on a night when it was near freezing. It took fifteen minutes to collect enough bracken ferns to make a two-foot thick mattress, but it was comfortable and warm.
You can use leaves, pine needles, dead grass or dry bracken ferns. All you do is make a pile big enough to set your tent or bivy sack on. This could damage the enviroment in some areas, so use common sense, and collect only DEAD vegetation. Also, scatter your materials in the morning, so they won't smother the plants underneath.
An important point here is that you have to know your enviroment, so you know you'll be able to find proper mattress materials. Otherwise, you could have a very cold night or worse. Also, gloves make it easier and safer to collect the ferns or grass. Try this first near home.
Knowledge Reduces Weight
Learn certain backpacking techniques, like the one above, and you can carry a lighter sleeping bag, less clothing, and even less food. Wilderness survival knowledge can help you reduce weight, but it also lets you travel the wilds more safely.
Learn which berries are edible, and you can eat as you hike and bring less food. I've eaten half of my calorie needs in the form of berries on some days in the wilderness. During a hike to Grinnel Glacier in Glacier National Park, my wife and I ate nine types of wild berries.
Researching the climate, and timing can help you reduce weight. You can leave rainwear home, for example, if you're in the eastern Sierra Nevadas in September (bring a garbage bag for emergencies). I sometimes plan trips to coincide with the full moon. I enjoy getting up at four in the morning and hiking by moonlight, and since I'm up and moving at the coldest time of the night, I can get by with a lighter bag.
Money Reduces Weight
Money will buy you lighter gear, and expensive backpacking gear is generally of very high quality. I didn't enjoy paying over $200 for my sleeping bag, but I've never yet been cold in it, and it weighs just 17 ounces.
Concentrate on the the larger items. A sawed-off toothbrush could save you 1/4 ounce, but a lighter shelter can save you pounds. Consider small things last. Buy dual-purpose items, like a poncho that can double as a shelter. Drink soup and tea from your pan, and you won't need a bowl or cup.
Leaving Things Reduces Weight
This can be the tough part of lightweight backpacking. Ask of every item; Can I get by without it? Stoves aren't necessary if you bring ready-to-eat food. You don't need a change of shirt or pants on a three-day trip. If you're not sure you'll be happy as a minimalist, go back to the money solution. Start replacing your things with the lightest alternatives you can buy. There are many ways to go lightweight backpacking.