Whether your students are preparing for a big essay assignment or a quick in-class effort, coming up with a topic to write about can be the hard part. Here is a fun activity I've used with my classes with good results. It loosens up the thought process, and is a nice change of pace.
Divide the class in to groups. Give each group a bag with six everyday items in it, such as a rock, a deck of cards, a piece of fruit, a magazine, a quarter, etc....Set a timer for two minutes and have the group pull one item out of the bag. During the two minutes, the group should come up with as many topic ideas as possible related to the object. For example, if the group pulls out the quarter, some topic ideas might be money management, saving strategies, summer jobs, economic policy, reward motivation, allowances from parents, getting paid for good grades....Tell the students to list everything that comes to mind without editing. The more ideas, the better. After the activity, have each group share of few of their best ideas for each object with the whole class.