So you've nailed down a destination, and now you're chompin' at the bit. Throw a few Jockey shorts in the backpack and off you go, right? Not so fast-any overnight trip requires a bit more forethought. And if you're headed on an extended tour on two wheels, remember, "less is more." Even if your week-long odyssey is on a full-blown touring bike, you'll have to make every inch of cargo space count (especially if there are two of you). That ice bucket will start looking pretty dumb after Mile Marker 3. We talked with Tom Mehren, author of the new book Pack Light, Pack Right! (available at www.mm411.com). Mehren's also a proponent of the less-is-more theory. Following are his main packing points:Heavy On The BottomStuff heavy gear closest to where the bag will be mounted on the bike. I like to use a three bag system on extended trips: one big sack for the large stuff, a medium bag for necessities and a smaller one for traveling fast and loose. (This one comes in handy off the bike.) The big bag should be weather- proof, durable and flexible enough to accommodate different loads on different bikes. Attachment points, stiffeners or frames help the cause too. The medium-sized bag should essentially be a stuffable, soft bag that can be rolled up, and I usually grab a backpack for light, off-bike excursions.