Latent heat of fusion can be demonstrated with a super-cooled molten solution of sodium acetate trihydrate and water. Sodium acetate trihydrate is metastable when super-cooled while molten, allowing it to be stored well below its melting point of ~58 degrees C while still a liquid. When agitated it will crystalize and begin freezing while heating up close its melting point of 58 degrees C in the process.

The sodium acetate trihydrate solution is stored in sealed reusable pouches and there are enough pouches for ~30 students to perform the experiment. CAUTION: the pouches get noticeably warm to the touch and can burn if enclosed and insulated while against the skin. 

To "reset" the pouches, boil them for ~30 minutes (or until no crystals can be seen). CAUTION! Do not allow pouches to rest against the bottom of the boiling container as they can melt to the bottom (i.e. keep a layer of water between the pouch and the container)

Sodium acetate (and carbon dioxide) can be created by mixing baking soda and vinegar. 

Latent heat of fusion