Filter, Heater, and Light.
It dosn't have to be fancy. For ease of use, I use a filter that uses the same media as my main tank. This way it forms an instant cycle. I just used the established media from the old tank. You can use a simple internal filter though if your budget is tight.
You will want a Light so you can observe the fish. You know what the heater is for of coarse.
You want the tank to have a bare bottom for ease of cleaning. I also through in some pvc pipe for hiding spots. You could also use plastic plants for those plant loving fish.