Spare Mesa Boogie, spare back, spare strong person, spare fingers, toes , legs - in event of crushing injury [size=4] Seriously - mains and the HT fuses. Also some pre amp valves and a pair of output valves. These days I would also take a spare soiid state head - something cheap will do. I must be lucky, all the valve amps I have owned (Hiwatt x2, Marshall, Fender, Vox, Sound City) have never failed at a gig.[/size]