Updated: Oct 2
I've tried working with several different kinds of treat-dispensing systems and I've observed many students -- work with them in classes, in a working session (therapy dog), and while working in and enjoying the outdoors. BTW, I own no stock in any of these companies and have not agreed to any endorsements; merely my opinion on product function.
I've yet to find an airtight treat pouch that keeps fresh treats soft. If you want to leave treats in the pouch until the next walky-walkies or training session, place them into a silicone reusable bag or some other kind of airtight container because if you don't, they will be rock-hard next time you go to use them.
1. My favorite so far. I bet I know what you're thinking, "that looks like a fanny pack!" You could make that argument but please observe that it's a flat-fitting belt and you can't beat the function. Hands-free, sleek and adjustable to your body so you're not constantly bumping into it, you can hide it under your shirt or jacket (so your dog isn't radar-locking on the bag and trying to get at it), zips closed, waterproof, fits most phones, pockets for poo bags, and removable carabiner(s) to attach other items like a leash or whatever. Our trainers often wear these in classes to keep their hands free, and they come in a variety of colors. (https://www.doogusa.com/products/doog-walkie-belt-navy-yellow-improved-design)
2. I prefer a sleeker bag as opposed to the old school cup-style pouch because I'm prone to knocking it and possibly sending treats bouncing about. Best to avoid the pouch that holds everything but the kitchen sink otherwise you'll be fumbling for treats, risk stuff falling out (phone), gets bulky, and attachments bounce and clang around as you move. In the case of the cross-body bag--when it's heavy it swings around into your dog's face when you bend over. To each their own though; you might have your reasons for carrying more. That being said, the following are recommended as slightly better in design than others; note that they have both a cross-body and belt clip option, a method to seal off treats from spilling out yet treats are easily accessible and bag is compartmentalized so you can keep your stuff clean & dry (hopefully):
This bag (above) is a basic style that is available from many different manufacturers. Just look for the basics we talked about earlier and you should be fine. Wear it slightly behind your side so that when you move your arm back, your elbow doesn't knock it around, and the bag isn't immediately in your dog's sight (though they can likely smell it no matter where you place it [on you]).
These next little silicone goodies are simply just a food dispenser, and easily washable. Marketed as BPA-free, they still don't keep fresh treats soft if left in the pouch. I noticed several reviews where customers complained about the device falling off -- remember what I said earlier about those side pouches getting in your way? Maybe it's just me <sigh>
Lastly, you could always use a sandwich bag or even better for Mother Earth, a reusable silicone bag stuffed into one of your pockets. As unsophisticated as that may sound, you're actually better off when your pup can't readily track the bag and now your rewards seemingly come out of nowhere. This helps make your training less conditional on whether or not "you've got the bag" AND, you'll get more focus on YOU!