What To Pack It In > Dual-Purpose Travel Bags
Somewhere between the packing/organizational efficiency of a top-drawer business bag and the carrying comfort of a suspension-system-equipped leisure bag lie the dual-purpose offerings. Such bags offer features from both categories: multiple compartments designed for optimal packing, coupled with a carrying system that distributes the weight across both shoulders.
Travellers often find themselves occupying the same middle ground. Leisure travellers might well wish for a more compartmentalized organization than is typically found in bags with high-end suspension systems. And ultra-practical business travellers (who are not put off by occasionally exhibiting what some might consider an "un-businesslike" appearance) might seek luggage that offers the option of being carried on their backs (i.e., like a backpack). The latter can also be appealing to those who find themselves — for whatever reason — incapable of carrying a bag on one shoulder for extended periods of time.
Make no mistake: dual-purpose bags are compromise solutions. They gain weight and lose storage space in order to add backpack straps and the panels that conceal them when not in use. They lose the sophistication and comfort of a full suspension system (with padded hip belt, sternum strap, supporting struts, etc.) in order to provide more compartmentalization. They will never be as optimal as bags designed for one or the other specific purpose. You can't eat double bacon cheeseburgers with fries and stay thin. But for those who don't travel enough to warrant owning both types of bag, or for those whose trips contain elements of both usages, they may well be ideal. Fortunately, there are at least a couple of products that fill this niche admirably.
Recommended Dual-Purpose Bags
An early entry in this category was the Tough Traveler "Tri-Zip #4032". Its manufacturer may be best known for its legendary "child carriers", but also makes a considerable variety of bags, all of which feature commendable craftsmanship.
The Tri-Zip, pictured at left, measures 20 × 13 × 9", well within the usual carryon limitation, and weighs 3.5 pounds (1.59kg). It features a strict rectilinear design, Cordura construction, three main full-length packing compartments 
(two of which have extended zippers that allow them to be opened flat) plus an outside zippered front pocket for convenient access, (removable) aluminum stays for backpacking support, full inter-section padding (also removable, should you wish to increase storage space, but great for laptop protection and to provide some structure to the bag for packing purposes), and more. Plus, of course, hidden backpack straps (shown exposed for use on the right). When I saw this bag for the first time, I could think of only one potential improvement (a change in the design of the internal tie-down straps), which they immediately implemented. Tough Traveler sells this bag, in nine colour choices, for $225 (which, considering the labour necessary for its construction, is surprisingly reasonable).
The Red Oxx "Sky Train", another quintessential dual-purpose bag, comes from a company reknowned for its "take no prisoners" approach to rugged bag construction.
Pictured at left, the Sky Train also measures 20 × 13 × 9", allowing it to be overpacked a bit and still fit within carryon requirements, and weighs 4 pounds (1.81kg). Its rectilinear design includes two main compartments (both with storm-flap-protected wrap-around zippers, plus tie-downs in the larger main section), an outside full-length zippered pocket,
and an internal 9 × 12" floating pocket for loose items. Handy grab handles on the top and one side ease stowing the bag in tight places (like overhead compartments), and are comfortable for hand carrying when desired. The backpack straps (shown at right), along with their attachment points, slip out of the way behind a zippered panel when not in use. Construction is 1000 denier urethane-coated Cordura nylon fabric, with #10 YKK chain zippers throughout, and bomb-proof D-rings for the shoulder and backpack straps (included is the stellar "Claw" strap and a heavy-duty luggage tag). All seams are double-stitched and bound with #92 bonded SolarMax nylon thread. The discreet use of inter-compartment closed-cell foam padding gives the bag some structure for packing purposes, without compromising flexibility. The Sky Train, available in twelve different colours, sells for $255.
Full disclosure: I provided some consulting advice to the manufacturer of the Sky Train, though I received no compensation for this, nor do I obtain any monetary benefit from the sale of the bags. I did get a free Sky Train, however. Actually, lots of companies send me bags for review, though few of them ever show up on these pages.
So which of the above two bags is "better"? As you might expect, there is no unequivocal answer: it depends on your individual needs. On a scale ranging from "business" to "leisure", it's probably fair to say that the Trip-Zip leans slightly more toward the business end, and the Sky Train in the direction of leisure/adventure travel. But it's really more useful to consider how specific details meet your needs. The Tri-Zip has three main compartments vs. the Sky Train's two, so if you need a larger space in which to pack a bigger clothing bundle, the latter would be preferable; the former is a better choice if you want more compartmentalization. The Sky Train is more strongly constructed (and more tolerant of inclement weather), so will better satisfy those looking for "bomb-proof" longevity. But the Tri-Zip costs a bit less.