I was learning about this in one of David Harvey's lectures on Capital, which are on youtube - the problem, in part, was that gold is not a neutral, abstract thing, it's an actual commodity, so if you have a gold standard then 'which countries have gold' is a live issue.Nixon de-coupled the dollar from gold value in 1971, allowing the US to print as much money as it wanted, effectively destabilizing the global economy. I worry about paper assets held digitally and what might happen in the event of cyber attack, bank failure, or stock market crashes.
As for the topic of the thread: yes, I always carry a tenner, but as often as not I end up spending it on other people (bus tickets, taxis, bottle of water) when friends or passers by are in a bind and have no cash on them.