In my BOB is a Kel Tec Sub 2k folding rifle that takes Glock 17 mags. It is compact and fits nicely in a backpack or small duffle. On my person would be the Glock 17. A combination of 17rd and 33 rd mags in the BOB that are interchangeable. I only have to carry one caliber and one style of mags. I feel that the 9mm is the "swiss army knife" of calibers. A nice balance of weight and power.