A gold bar is 12.4 kg (27.3 lbs). It's worth over half a million USD currently. Is that heavier or lighter than the same amount of money in bills?

According to some guy on the internet who seems to have done the calculation with a bit of care, a million dollars in $100 bills are around 20 lbs. (See "joe" in https://answers.yahoo.com/question/index?qid=20090718165259AA6Xvwc) Half of that is 10 lbs.

So if you're bugging out on foot with half a million dollars, try to fill your backpack with Benjamins -- this is assuming US currency is stable. I'd make sure to include some small bills in case I run into a soda machine.

However, a gold bar allows you to plunk it down on a banker's desk with a great deal of drama. If you're a Nazi hunter or something, you can make a bigger statement with a gold brick than with a suitcase of money.

Some conspiracy theorists believe that aliens use gold as fuel for their spaceships, and they genetically engineered mankind to covet gold so we can find more of it for them. (We're sort of like truffle pigs, but for gold.) If the "end of the world as we know it" situation involves alien invasion, it's hard to say whether the gold would be of benefit. Maybe they'll reward you for filling up their gas tank. Or maybe they'll just take your gold and eat you -- hmmm, survivalist tartare!