I also carry multiple ways to play music with me. SC2900’s with Engine are my main method, but if my laptop went down I have Thumb Drives with enough music to get me through a gig, plus a whole load of CD’s. If one (or both) SC2900’s went down, I have traktor on my laptop with my MC6000. Also carry a MP3 player with me. If both the SC2900’s AND the MC6000 went down I carry an NI Audio 2 that I could use traktor with, and I carry a spare 2 channel mixer with me.
Never had anything fail on me, but you can guarantee if I didn’t have a backup something would go wrong!!