I just came back from a lan party (3man), we had 12 bottles of mountain dew and it still didn't manage to keep us awake. :p
At some point you need more than sugar and caffeine to keep going, snickers bars are in fact one of the best ways to get actual fuel (peanuts) into your body (not energy bars because they are just moar sugar).
Caffeine speeds up your metabolism, sugar is easily turned into energy. The combination of caffeine and sugar does give you energy but it also eats up your limited stores of carbs and when those are gone you crash, hard.
Next time you have a lan party and you want to wipe the floor with your friends bring caffeine, sugar and trail mix.