I had borrowed one of these Nathan packs from a friend for a 5k and fell in love with it.  I recently started running and training for 5ks and I was using regular fanny packs and they were just annoying with everything bouncing around.  After using my friend's pack, I purchased this one for my most recent race and it is awesome!  Big enough to fit a cell phone, keys, I.D. and even a luna bar, but small enough to stay put.  I am 5'1" 117 lbs and it's a great size for me.  Nothing moved when I ran.  The pack didn't budge!  I love it and recommend it!! Also, having Amazon Prime shipping is the best.  I got the pack in 2 days with free shipping.