A cake leveler saw looks like a hack saw. Mine looks like this one:
https://www.amazon.com/Leveler-Calia...68545840&psc=1
It's used for cutting the dome off of the layer of cake, so that the layers lie flat and level when stacked. You can also level a cake layer by using a serrated knife and eyeballing it.
Cake "belts" are insulated straps that wrap around your cake pan. They help to keep the edge of the cake layer from cooking faster than the middle, thereby creating higher layers and no dome in the center. Mine look like this:
https://www.amazon.com/Regency-RW002...%2C1744&sr=1-6
A set of small and large offset spatulas are really good tools too. They make frosting a cake much easier. None of these tools are very expensive.