If you backpack in the Sierra, you are required to carry a bear canister in many areas. What is a bear canister? It's a container to protect your food from bears and other animals. Bears are incredibly smart. The canisters are the best way to foil bears. If bears or other animals eat your food, your trip is over. I have not seen any FatDonald's in the back-country :)
The canisters don't have a lot of space, so you want to repack items to make them smaller. I eat Mountain House when backpacking and camping. They are tasty and filling; however, the packaging is large. I repackage them so I can fit more into the canister. This goes for everything with a smell. Toothpaste, deodorant, and soap. Now I don't repackage those items. I buy trial sizes which are perfect.
Pros for using bear canisters:
* My food is safe from all animals
* Convenience - I don't have to waste time setting up a system to hang food
* They double as a chair
* Required in many areas
* Durable - they last forever
There are some cons:
* Adds weight
Obviously, I feel the pros outweigh the cons.
How to use:
There are two screws on the lid of the canister. To open the lid you need a coin. I tape a penny to the top of the lid. That way I know where it is at all times. Simply fill the canister with food and all items with a smell and close the lid with the penny.
At the campsite: Wedge the canister under a rock or between trees. Believe it or not, there have been reports that bears get pissed off at the canisters and will bat them around several yards! Store the canister at least 100 feet from your tent. The whole idea is to keep bears away from you.
A word to the environmental nuts: I use a bear canister to protect my food, not to protect bears! I do NOT think throwing a rope over a tree to hang food hurts the tree! In the old days they use to hang people from trees. Don't tempt me.