My normal routine is a Glock 22, 23 or Colt Gov't on my waist, backed up by a Glock 27 on my ankle if I am wearing long pants.
Many folks subscribe to back up guns, but most usually in the form of a .22, .32, .380 or the like. My particular thought on this subject is that if your primary gun goes down for whatever reason, your back up gun just became your primary gun. So.....if I wouldn't carry that .22, .32. 380 et al as a primary, why rely on it as back up? Just food for thought..
"If you are ALWAYS ready....you never have to GET ready....."