Thanks Brangdon. I'm thinking of 'bugging out' of the kind we did on escape and evasion exercise in the army. I.e you are in enemy territory after escaping from being a POW, or trying not to become one. So the shout "BUG OUT!" means 'the enemy have found our hide; run with whatever you have on you'. No time to pack.
I'm not sure if that is the meaning here; this is after all not a military web site and also an american one.
So far in the UK the tornados have left the houses standing and you wouldn't have to head to the door in the clothes you were wearing. With global warming watch this space to see if that lasts....
But as you say; having overnight bags packed will only make life easier.
The Sock