You need a filter rated for 30 gallons preferably. AquaClear is a great brand.
A 100 watt heater would work well, Aqueon or Eheim are really good.
Lights can be anything you want if you don't want live plants. If you want live plants I would suggest going with at least T5; that would give you the most options.
A liquid test kit by API for ammonia, nitrites, nitrates.
Gravel Vacuum. Any brand.
Gravel or Sand. You generally want 2LBS/Gallon, but you can go less or more if you want.
I would suggest getting a glass top also.
Those are pretty much the basics, but then you need fish food, water dechlor, decor, etc.