The yes/no game
There is just one rule; you can't say yes or no. The Bong game (also known also the yes/no game) Found fame on the Des O'Conner hosted game show 'Take your pick'. It sounds simple but is painfully tough even for the most articulate speaker.
A common problem in warmers is the reluctance of some learners to expand on points made, with follow up questions being answered in single words. This is a tricky but very fun way of drawing out more language, and many classes I taught have ended in fits of laughter through this game. It's also fantastic practise for fluency as your students can ask the rapid fire closed questions required to throw the contestant off balance. You can increase the authenticity by bringing a gong in to class.