+1 on filling with hot water if you're out of sanitizer.
Prior to the excellent no-rinse sanitizers available now, my pre-filling keg sanitization method was to pour four cups of very hot water (right at the point where it started to boil) into the keg, lock the lid in place, and shake. Shaking caused the keg to pressurize with steam. After a few minutes I then attached a tap and opened it up to allow hot water to flow through the liquid out connection, just to be sure the inside of that tube had exposure to 180+ water.
Remove lid, dump remaining hot water, run cold water on the outside to cool it, and fill with beer.
But remember, just like the coffee at McDonald's, the water is hot and can burn you!