Having suffered an amp failure mid-gig I now take no chances and have spare pretty much everything: bass, amp, leads/cables, strings (a used set for emergency use) and as many plectra as my holder will hold. The only thing I don't have a spare of is an XLR cable, as the DI is usually the last resort in the size of venue we normally play and I haven't had to use the one I have yet fortunately (touch wood).