Ultralight backpacking is a popular activity, and, if you're so inclined, you can easily invest a great deal of money in lightweight equipment -- the kind specifically made for the sport.
Titanium is used for pots, pans and eating utensils, and is much lighter than stainless steel or plastic. Tooth powder, measured precisely so that you only carry enough for your trip, is lighter than the lightest tube of toothpaste. The most expensive sleeping bags also happen to be the lightest weight.
But ultimately, ultralight backpacking is about choices. And each person has his or her own opinion on what's necessary. For example, when you're deciding on how to prepare food, you have several choices of stoves. Liquid fuel stoves are commonly used by backpackers, but canister stoves are smaller and lighter.
Want to go even smaller and lighter? Choose an alcohol stove. It uses denatured alcohol as fuel, which you can carry in a lightweight soda bottle. The drawback is that it takes longer to boil water and you have less control over the temperature. If you want to go even lighter than an alcohol stove, fuel tabs are the lightest option of all, but they have a strong odor, can be tricky to light and leave residue on your pot. They also take longer to heat up, and again, you have less control over the temperature.
The same pros and cons must be weighed for each item on your camping list. For example, down sleeping bags are lighter-weight than synthetic bags and compress into a smaller size. But when they get damp, they lose insulating ability and take a long time to dry. Synthetic sleeping bags provide the same amount of warmth and are heavier. But if they get wet, they dry much quicker. Synthetic bags also are generally more affordable.
You easily can spend your next two months paychecks on ultralight backpacking gear, but that's not a prerequisite for the ultralight experience. You can dramatically reduce the weight of your gear without buying a single new piece of equipment. How?