Placing pure sodium in water & watching it explode & fizz out it super entertaining. Also, watching a magnesium strip burn over a bunsen burner is an excellent way to observe an exothermic reaction. One of my favorites is pouring sulfuric acid over sugar and watching a purely carbonic solid mass emanate from the beaker. Placing pennies manufactured after 1984 in hydrochloric acid & allowing them to sit overnight produces an interesting result, but you must make 4 indentations with a scalpel on the edge of each penny before placing them in the acid for this to work. I won’t disclose the end product just in case you actually perform this experiment. These are a few if the fun activities my chemistry class performed through out this school year. If you need further details, I’d google them.