Me and some other friends used laptops (think they were IBM ThinkPads), PCMCIA Ethernet adapters (maybe from Xircom?) and thin Ethernet (coax) to play multiplayer DOOM on a Reno Air or AA flight from San Jose to Austin once. I think we were using IPX for networking and we just strung coax between the seats.

Needless to say this was before 9/11 and the flight attendants took it in their stride.