Divide the class into four groups. Each group is given a maximum syllable, a set of consonants and a set of vowels. Members of the group work together to create as many words as possible in five minutes, given their set of segments and restrictions. Segments can be reused as often as desired and words are to be written in orthography.
After the time is up, the class works together to strike any words from each group's list which violate the restrictions either by exceeding the maximum syllable or using a segment which is not in the designated set.
Be sure to discuss any circumstance which made one groups' task more difficult than another's: life isn't always fair, afterall!