Let's take cheer, for example. What part of speech is it? It can be a noun or a verb.
Now ask your student to make it into an adjective: cheerful.
How about a participle: cheering.
An adverb? cheerily.
Do this for any words that pop into your mind. Here are some that popped into mine.
adjective: celebrative, celebratory
adjective: excited, excitable
Another idea is to let your students think of the words, morphing them in as many ways as possible. Then ask them to check a source, such as www. dictionary.reference.com to see what others there may be.
In addition to becoming more savvy with parts of speech, they will see the versatility of words and build their reservoir of vocabulary!