I believe that the bear regulations are oriented toward food storage while camping, not while hiking. There are bear boxes located in the backcountry of SEKI along the JMT for food storage while camping. These are all within pretty easy hiking distance of one another. North of SEKI, bear boxes are only located in developed areas (i.e. Reds Meadow, Devils Postpile, Tuolumne Meadows) and in Little Yosemite Valley. There are several maps and lists online that show the locations of these boxes. Some research into the facts would be a good idea before going into the Sierra. A good place to start is the SEKI Bear Management webpage found HERE and the SIBBG website at SIBBG . There are links to list of where bear box locations are. Here's a quick link to a list of bear box locations throughout the Sierra, BEAR BOX LOCATIONS.
There are areas along the JMT where bear canisters are not required for food storage, they are only recommended. There was an excellent map that was produced by the USFS last year (2007) showing all the regulated areas and bear box locations and trails in the Sierras. It was a great overview map in geneal of the Sierra. I was going to provide a link here, but the map has vanished. Here is a link to an article about the map, BEAR BOX MAP. Fortunately I downloaded the map so I do have a copy of it.
One last thing. The Bear Box location in SEKI are generally in heavily used areas that will be very crowded with people during the peak season. Unless you like camping in the backcountry with crowds, I wouldn't plan on using them. Using a bear canister provides a degree of freedom and safety (for both people and bears) while traveling in the Sierra. The main bear canisters available are 9" or less in diameter. Depending on the height of the bear cansiter and the size of your pack, you may be able to fit the cansiter in sideways in the bottom of your pack. If not, as long as your pack is greater than 9" in diameter, the cansiter will fit standing upright. In my Vapor Trail long, it's not quite big enough to fit the Bearvault BV400 sideways in the bottom, so I have to stand it upright.
Hope this helps.