Gold has value as a form of money because of its properties. Most importantly, it can't easily be created, despite alchemists' best attempts over the centuries, and can't be found in relatively large quantities, so is not subject to inflation like paper money. Then there are other useful properties like its inertness (doesn't corrode over time), and its ability to be easily shaped into coins and divided into accurate smaller pieces (unlike diamonds for example).
However, this is all reliant on there being a perceived need for a form of money. The only alternative I can think of is barter, which is highly inconvenient in anything other than small communities. So on the assumption that there is a need for a form of money, gold has most of the desirable properties to fulfil that role. In small closed environments like prisons and POW camps, things like cigarettes have at times fulfilled that role.
If the world devolved into some sort of post-apocalyptic mess, initially other things like food and water for survival would be more valuable, but eventually there'd likely be a need for some form of money again. Who knows what it might be though. If all technology had gone, then old technological gadgets might be useable, again on the basic premise that they'd be in limited supply and not able to be manufactured. Not readily divisible though, so maybe the currency would be something like 1 Playstation = 10 Gameboys = 100 MP3 players, with 10 Playstations being one large plasma or LCD TV, and so on. You'd want big pockets to carry it all around though!
GP