As an investment, perhaps going long on precious metals makes sense. But in a true apocalypse, who will care about blocks of gold? Some warlord?
In the much more likely scenario of a month long power grid faiilure, a terrorist's dirty bomb, or anything that disrails our economy for a spell, small common denomination US coins with known gold and silver content are going to be the currency of choice, aka "junk silver" or pre-1964 coins. You can buy these at coin shops, rates are published online so you can't get screwed too bad.
Giving someone a few silver dimes for fuel and food may be a lot easier than whittling off a shaving from your gold bar.