ok I have been doing tons of reading of the forum and articles and backpacker and have a good idea of what gear I need and have started making a list..I am brand new to hiking let alone backpacking but am hoping to start building up to doing 100 miles of the john muir trail next august.I was looking at backpacks at REI and found a couple I actually liked(just informally no sales rep help)One, was large enough to accommodate the canister one was not..this started me thinking, can one strap the canister to the outside of their pack? or do you need a pack large enough to place inside? any pros or cons either way?