I carried in a fanny pack once, seriously didn't like it and went back to a strong side kydex holster on a good belt. I suppose it would work for some firearms, but my G-19 was not one of them.

When I'm camping or hiking nowadays I generally carry my sidearm in a Hill People Gear Kit Bag or Runners Kit Bag. I suppose it says "GUN!" a bit more loudly than a lumbar pack but on the trails it's never garnered a second look. It's super comfortable and surprising about as fast to draw from as IWB. The regular Kit Bag has lots of room, and it carries the load very well. Without really overpacking it I can carry a full sized hangun (even an HK USP45 Tactical with a Surefire X300 Ultra!), spare mag, my Surefire E1B Backup flashlight, a notebook & pen, assorted fire gear and a pair of gloves. When I camp alone in more remote places I sometimes wear my HK P30S IWB and carry an HK USPf9 with an Inforce APL in the Kit Bag.

NOTE: No affiliation with HPG, just really like their stuff.

I'm contemplating the purchase right now of an HPG Snubby Kit Bag. I can wear it with my ruck on my back.

I have two HPG packs, a Runners Kit Bag in OD Green and an Original Kit Bag in Foliage. I really love them both! The only bummer is that black isn't offered; they did a limited run of the Recon Kit Bag in black but it sold out just hours before I went to order one! They're really awesome packs! Very very comfortable and stable. I hardly notice it after wearing it awhile. It's actually not even all that hot. The back part is mesh and front allows some ventilation.

You don't mention whether or not you want to use if for CCW or not. I considered the Snubbie but the smallest sidearm I would ever carry is an HK P30S, and the guys at HPG said they doubt it would fit. I'm actually glad I went larger; you can carry a smaller firearm in the larger bag but not the other way around. If you truly do just plan to carry a snub revolver it would be okay. I think a Glock 19 will fit but there's not much room for an extra mag. Initially I was concerned that it would be hazardous to carry a gun with no safety in a pack without a holster but the inner compartment protects the trigger very well. Even so I carry in Condition One (ie. cocked-and-locked), and there's no way the safety will come off in the bag.

The Original is about 1.5" thicker than the Runners, and it's a bit expandable. In the Runners I can get my sidearm (either a USP or P30S) plus one mag, a small flashlight, my wallet and keys, but really no more. The Original is enough larger that in addition to all that I can also carry a notebook, pen, some fire stuff and a pair of gloves...maybe a bit more even but I don't like to overstuff it.

If you're interested here's a video from a guy I'm acquainted with doing a review of the HPG bag he carries.