Aluminum works well, but any metal will suffice. Using a pair of tongs, heat the metal cylinder over a bunsen burner flame for several minutes until it is uniformly heated. Then quickly drop it into a freshly opened bottle of root beer and stand back. You will see a fountain of foam violently shoot up into the air with heights exceeding 60 cm. Like a volcanic vent, it will shoot straight up into the air, and then cascade back down, losing at least a liter of soda in the process.
Root beer works very well, since it seems to produce more foam than other types of soda.
The bottle should be placed in a dishpan or other shallow basin to collect the overflow. You might prefer to do this demonstration outside. Break the tablet into four equal-sized pieces. Wear safety glasses. A variation of this demonstration would be to quickly place the filled canister in the upside down position in a container of sand and quickly cover it with varying depths of sand.