I have one of the rare Mystery ranch "Asia Pacific only" 1 Day Assault Pack bags, which is a cross between the more mature 3 Day Assault Pack and the more recently released ASAP Pack.
I also have one of the Cinch straps, for comfortable wear and quick release of a pack whilst wearing a loaded plate carrier.
Great kit. The particular accessory that had come to my attention was the Removable Stick-It flap, seen here in Coyote, mounted to my black 1DAP. The Stick-It is a detachable beaver-tail that mounts to the bottom of a compatible pack to offer external storage when you've either gotten too much stuff, or just something too big for your pack to carry.
Built with 500D Cordura for long-haul durability, which I've come to expect from pack-makers, and fitted with mil-spec 1" webbing straps, Mystery Ranch have gone all out on the both the construction and the hardware. The buckles have a clip-in end, for fixing to MOLLE loops or other webbing on your pack, as well as a spring loaded friction lock for the working end of the buckle.
This kind of attention to detail as well as using better-than-standard fittings is something I love about Mystery Ranch. You pay for it, but it's worth it. The Stick-It attaches to its host pack with four press-stud closing loops of webbing, which feed back into the accessory by extra loops of MOLLE style webbing sewn into the Stick-It's interior. Those press-stud loops allow you to attach it to the bottom of any pack with MOLLE on its base.
I've put it on my Platatac Light Field Pack in place of its "Office" Admin Pack, or in fact as well as it. It also fits the Propper UC Pack, and the old standby the classic Platatac Bullock Echo, though the Echo already has a beaver-tail attachment built in.
The Stick-It has a couple of other interesting features. It is constructed to have expanding baffles in its Center line, in case of very bulky loads, with plastic inserts to stiffen the sides and carry the weight more evenly. You can really fit quite a lot into this, and is is the smaller of the two sizes offered. It also had a set of drainage grommets in its base, for those times you've taken a dip or been caught in a monsoon.
Another very forward thinking feature is the sheer length of the webbing for the attachment straps. This both lets you place the buckles anywhere from right at the back of the pack, to all the way at the front for quick release options of your over-load without shucking the pack propper. They also come with hook-and-loop keeper loops, to bundle the excess webbing up tight and out of the way for snag free utility.
The small Stick-It is perfect for stowing bulky times, like an Ops-Core bump helmet, a bundled jacket like the Platatac Harry 1.2 Softshell or the like. It can easily cope with even larger items, as long as you're comfortable with the, sitting out over the top of its top lip. The construction is hefty, and I suspect the weakest point would be the clip on the buckle. I've never had any trouble carrying my every-day items, let me know if any of you try lugging a ammo-can with yours.
The Stick-It isn't usually available as a stand alone item, but can be found in the Mystery Ranch Gunfighter pack, or through Hornest.