From 26C3 Public Wiki
Club-Mate
What is it?
A mate ice tea drink. It has a fresh, herbal, not too sugary flavour and wakes you up like nothing else.
It's made in the south of Germany and well known in most hacker conferences.
Also avalibel as Cola and Ice-Tea version.
clubmate.de
Where to buy at the 26c3?
At the bar.
At the Edeka in the Alexa shopping centre. One bottle costs 79cents
After 26c3 Brauerei Loscher or at next Summercamp ICMP(5) near/in Münchsteinach.