Back when I was younger, my mom shared with me a story of how a guest at a dinner honoring Christopher Columbus questioned whether Columbus should be considered great for discovering America. After all, the guest questioned, anyone could’ve set sail and eventually discovered land. In response, Columbus challenged this guest to try to stand an egg on its end without any supports. Try as he might, the guest could not. When he finally gave up and dared Columbus to try it himself, Columbus lightly cracked the egg on one end so that it would stand by itself—and at that moment, everyone understood: it takes someone special to figure out how to do something, after which anyone can do the same thing.

Let me share with you one of those, “Well why didn’t anyone else think of that before?” items: the Tom Bihn Convertible Packing Cube.

First, take a look at their regular Packing Cube:

A pair of Tom Bihn Packing Cubes.

Notice their ordinariness, their simplicity. The Seattle-based manufacturer (and there really is a guy named Tom who designs all this stuff) uses a Japanese nylon called Dyneema for its packing cubes, which come in various shapes and sizes and are designed to snugly fit in Tom Bihn bags.

Now, take a look at their Convertible Packing Cube:

The Tom Bihn Convertible Packing Cube.

Same fabric, same general shape, but with one difference: The Convertible Packing Cube has D-rings on each side of the bag. Snap a luggage/bag strap to both ends, and all of a sudden, you have a shoulder bag!

Because of its simple but sturdy construction, you can really stuff a lot of things in the bag.

The Convertible Packing Cube can easily hold all the items you want to carry for your day’s touring, including a folding umbrella, facial tissue, first aid kit, travel book, wallet, and other handy items.

The dimensions are pretty large; at 13.5″ x 8″ x 3.25″ (34.5cm x 20cm x 8.5cm), you can easily smoosh a bath towel, afghan, or travel blanket in it and turn it into a little pillow. You can also carry things like socks, and underwear, or various items you want easy access to on your flight (and just toss the Convertible Packing Cube on the floor by your feet). Depending on the type of shoulder strap you use for your main travel bag, you can even use that as your carrying strap when you reach your destination and want to head out for the day.

Morgan wears a Convertible Packing Cube like a shoulder bag.

The Convertible Packing Cube is larger than a woman’s purse, but smaller than a bicycle messenger bag. And even though it only weighs around 3 ounces (100 grams), the fabric is remarkably sturdy. The tight nylon weave means it’s somewhat water resistant, in case you spill something on it. It’s not waterproof, though.

The cube has a diagonal zipper on one side and it’s a good place to stash your cell phone or boarding pass. Both the main zipper and pocket zipper are YKK zippers, which are very well made. As with all Tom Bihn bags, the zipper is solid, and you won’t have to worry about the fabric getting caught in your zipper pull.

If every item you take on your trip has to serve multiple purposes, this Convertible Packing Cube is your answer. Use it to store things in your main travel bag, then use it to carry stuff around once you’re touristing around.

Just a couple of things to be aware of:

First, although the Dyeema nylon is very sturdy, it’s also very thin. While this is great for keeping the weight of your bag light, it also means that the fabric itself provides almost no protection against anything fragile you put in the bag. Any electronics like iPods or cell phones—especially if you think the bag will get jostled around a bit—are probably best off having their own little protective cases. And while the bag has plenty of room for a larger SLR camera, unless the camera is in its own cushioned camera holder, you are just asking to have your camera dinged up if you just leave it naked in this bag.

Second, the dimensions of the bag are very rectangular, and the D-rings are only a tad bit above the center of gravity. And because the fabric is so thin, the bag lacks a structural frame—which means you want to take a little care when opening the bag while it’s slung over your shoulder. If you’re not careful, the bag (or one of the sides when you unzip the main pocket) has the potential to do a quick flip-over. Think of it like a quick stick-out of the tongue. If what you have in your bag happens to be a bit top-heavy, the item can spill out of the bag in a flash.

I think the second issue is something they could easily fix, if they move the zipper area up a little and place the D-rings higher on the bag. My preference would also be to have it actually be closer in shape to their very popular Cafe Bags. By having it taller than it is wider, you wouldn’t have to worry about anything accidentally spilling out of your bag.

Although you have the option to order the Tom Bihn Simple Shoulder Strap at the same time for $10 (and it functions perfectly well with the bag), I have another tip for you: Buy a 1.5-inch Quick Release Shoulder Strap from Timbuk2 for $5.00. It’s not just that the Timbuk2 strap is half as expensive; it’s that the shoulder strap has a quick release handle that lets you easily adjust the strap’s length with one hand. With the Convertible Packing Cube, I find myself adjusting the strap length all the time—wearing it as a shoulder bag when I’m just meandering, and loosening the strap and wearing it cross-wise when I want to huff it down the street.

The Timbuk2 1.5-inch Quick Release Shoulder Strap.

The Timbuk2 strap does not come with an extra shoulder padding, but chances are, you won’t be weighing your Convertible Packing Cube down so much that the Timbuk2 strap will dig into your shoulder.

The verdict? I think this is a fantastic little bag, and I love it! It’s so simple, yet serves multiple functions! It barely weighs anything, and it’s so sturdy. Best of all, it’s completely unisex. It doesn’t look or feel like a lady’s purse, so guys can feel just as comfortable using this as their day bag. I hope it’s popular enough that they keep selling it, and eventually expand the color line to include travel colors like black and olive, or fashionable colors like red (and I’d be ecstatic if they made it more vertical than horizontal, or addressed the location of the D-rings to provide a more stable center of gravity).

And $20 is a hard price to beat for something this handy. This product earns a solid A from me.