Another interesting thing about carrying the Glock...I took a Glock brand kydex belt holster ($12), trimmed it to fit in a small fanny pack, and sewed it to the back wall with a velcro loop for the stocks (I guess you can call Glock handles 'stocks'). Anyway, the thing is completely secure, makes the pack look and hang empty, and cross draws perfectly. That particular holster covers the trigger and has a retention detent. I usually carry a little belt pack for essentials for side excursions, sans big pack, so this will have good utilitarian value too.
Walmart's "Outdoor Products" smallest fanny pack fits sub-compact weapons like they were custom made. And, if you go at it with seam ripper, you can remove all the useless stuff and lighten them right up! Like I said before, I normally don't carry, but for doing trail work or hiking hot spots like my southern border, this should work out fine.