Heck yes! For every single piece of equipment used. From computers to microphones, speakers to dress shirts. You name it – I have a second one on hand.
Not only do I have backup equipment with me – it is the same piece of equipment that is used normally. There is no point in having the extra equipment there if your “backup” is of poor quality and does not work when you really need it.
Equipment not working one day is not a matter of “if” it will happen – but “when” it will happen. Fail to plan – plan to fail.