Well get all the decorations you want, gravel or sand (make sure to wash the gravel completley before adding it to the tank or you'll get very cloudy water), a heater and a filter (choose one that had a bio wheel or a bio bag, like ceramic), a hood that fits tightly over the tank so fish can't jump out, and proper lighting.
Make sure you also get aquarium salt, water conditioner, a net, and water test kits (not the stick kind as they aren't that accurate). If you have a fully cycled tank for your 8 gallon one, you can use some substrate (such as the gravel or bio wheel/bag) to help cycle your new tank a lot faster.