When I used to babysit, I had some very energetic kids that just would not settle down to go to bed. I used to think of a topic, animals for example, and they had to go through each letter of the alphabet thinking of an animal starting with that letter. By the time they got to Z for Zebra, they were usually fast asleep.
I modified this activity and made 30 different category cards, and 30 different letter cards (put doubles of easier or harder letters to differentiate). You could even manipulate the categories to whatever you are working on in class. I made different backs for each deck to help shuffle and separate, and laminated them for a long life. The kids love it! I even took it to uni the other day, and it had adults addicted!
One card from each deck is turned over at the same time, and the players have to think of a word in that category, and starting with that letter. Whoever guesses one first, wins that category card, and the player with the most category cards at the end, wins!