I call it a Bum Bag, but there are hip packs, fanny packs and others.
There are a huge number of reasons that I like this format. My choice is to run adventurously, or lead others into wild places, and for this a bum bag, in my view is the tool for the job.
I've been looking to replace my 25 year old bum bag for a good while, and I've finally found the perfect replacement in the Pack NW Ridgeline (Pack NW website).
Whilst the quality of this video isn't amazing (it was a pretty rubbish day on the mountain) - this I think gives a few ideas of the features that are important to me as a trail running, and mountain biking guide in wild places.