We actually always just went with coffee, even as teenagers. I guess as early millennials, we weren't yet the energy drink generation.
I 100% agree, though: alcohol beyond a beer or two isn't recommended for a LAN at all. Although I guess I have a "fond" memory of sitting there, playing Left4Dead with friends at a LAN, when one who didn't play himself at that moment piss-drunkenly leaned on my shoulders from behind, slurring directly into my ear: "You have to shoot them! Shoot them! You have to shoooooot them!!"