Another vote for Doggone Good ones. I love them. I wear two on a belt, so I can just grab it and clip it round my waist, no matter what I'm wearing. Two because I use the left hand one for treats and the right hand one for other things, like balls, a dummy etc. They're really roomy and can hold five or six standard tennis balls. They wash very well. I love the zipped back pocket for keeping my phone and keys. I put clicker in the front. The pouch inside has a bit at the back (which is far larger than it first seems) so you can have two different types of treats. And a roll of poo bags goes in each one, so I'm never short of those. I clip my mittens to them in the winter, if my hands get hot.
The only tiny niggle I have is that the "dispensing hole" for the poo bags doesn't really work... I find the roll of poo bags pops up and out of its little holder. But it's hardly a big deal, I simply don't use it, and take the roll out when I want to get one.