For me, a long time is:

* The amount of time between emptying my last beer and the bartender bringing me the next
* Waiting for the old lady in front of me at the grocery store to buy $200 in lottery tickets when all I am buying is a can of soda
* The amount of time until my next vacation

In all seriousness, 2-3 weeks for me, although I am prepped for quite a bit longer. I have enough food/water/firewood for about 6 months if I bug in.