Elf and Saftey would probably preclude private use of any sockets in venues, but it's something I have mentioned before at other festivals.
Phone based internet is taking over from wifi links?
I believe the library in town (Blackmore gardens area) has wifi but you may need to register and pay.
One festival did have a stewarded area for charging phones, and lots of power sockets - you left yours there, got a ticket and went back for it later. Can't remember where it was though! Might have been Towersey?
Someone with a tiny Honda generator and an array of sockets could set up a changing station as a sideline! Output 1000 watts, power required per laptop = 50 watts? - you could do do twenty at a time! Expensive on fuel though!