Variability in potential field bag design is nigh-infinite and depends entirely upon preference.  Asking yourself, “What do I want to use the bag for?” will help identify which is right for you.

For instance, for long trips you’re going to want padded strap(s) and probably would benefit from a full backpack with a waist buckle for stability, while the short-term day-traveler might prefer a single-strap bag designed to be worn as a sling.  Some will want hydration built-in, while for others this is less an issue.  For those who see their needs changing over time, choosing a bag with PALS webbing allows you to add pouches, pockets, and equipment where you need them.

As for me, I have a couple of personal favorites that have served me well in the field – one a sling-style, one a messenger-bag style – that I can vouch hold up under punishment.

The first, pictured at right, is a Maxpedition Jumbo Versipack.  Military-spec and rugged, this top-flap, sling design is very versatile and allows you to shift the bag in front of you to access contents and then back around to your back for travel with only one hand.  With ample PALS webbing, I was able to add exterior pouches for my multi-tool and first-aid gear, and you can even add a pouch that clips between the bag’s shoulder strap and the bag itself, positioning the pouch right at your chest, for things you access regularly (monocular, Swiss army knife, chapstick, etc.).  The built-in water bottle/radio pouch is perfect for a Sigg bottle.  Two enthusiastic thumbs up.

(Note: Now, (as opposed to when I picked up mine back in 2008,) the Versipack even comes in a spectrum of colors.)

The second bag, (depicted at the top of this post,) is sold by US Cavalry: the S.O. TECH Mission Go Bag.  While more a traditional shoulder/messenger bag-style, the Mission Go Bag is also mil-spec, has more PALs webbing than the Jumbo Versipack (which you can see I took advantage of), sports four large interior compartment dividers, is plenty rugged, and does have one particularly handy ace-up-the-sleeve.  With a clever placement of snaps, the shoulder strap actually becomes a belt, and after only a few moments of adjustment, the bag may be worn around the waist.

(Note:  While fine on its own, if you’re picking up one of the Mission Go Bags and plan to wear it over the shoulder for extended periods of time, I’d recommend augmenting it with one of Maxpedition’s shoulder pads – I think they’re the best out there.)

So, the punchline?  They have different strengths and weaknesses.  The Jumbo Versipack has a little smaller interior compartment than the Mission Go Bag but is easier to access on the fly.  Personally, I ended up using my Versipack as more of a simple survival/hicking pack, and the Mission Go Bag was more useful for scientific equipment.