A heat gun is not required to to make epoxy river tables or similar types of applications, but it can be helpful for flow, removing bubbles, and creating special effects. A hair dryer can also help perform the same task, but may not be quite as efficient.
Propane or butane torches can also be used to help promote better self-leveling, and bring bubbles up to the surface, but this method is not ideal. It is extremely important to keep the torch moving, and keep it a few inches from the surface of the epoxy; there is a risk of singing the surface of the epoxy, or leaving an inconsistent finish from scorching.