As a warm-up activity, I printed this list of 50 Impromptu Public Speaking Topics, cut them into individual topics, and put them in a basket. Students had to draw a topic and deliver a speech. The activity was such a hit, my students were begging me to let them take another turn.
Being able to write a solid persuasive speech comes second to the ability to deliver a quality speech. This article on Scholastic.com breaks down the speechwriting process into simple, workable parts. As an added bonus, teaching students to write a persuasive speech, in addition to delivering one, broadens the range of Common Core State Standards you would be bringing into this unit.