A laptop has a battery pack and can be run on the battery for some time. It needs recharging which will use electricity but not as much as a desktop computer. The amount of power any computer will...
Very little ! About the same as an ordinary 100W light-bulb. Most of the time, it's just sat there in 'stand-by mode' waiting for someone to insert their card.
As this is outdoors, juice has to be piped in, from generator trucks- which consume Gas or Diesel fuel- as Carnivals derive their power supplies. Rock amplifiers are potent brutes- a 500 Watt amp is...