They are not all the same, some people have a small substrate some have none. Some people have a couple of small pieces of LR in theirs some just have a PVC pipe. A HOB filter is necessary with a heater and a small powerhead. You can keep some type of sponge or other type of filter media in either the tank or the filter for your bacteria to live on. And thats pretty much it.
I have a 10gal bare bottom tank with 2 small HOB filters, one runs a carbon bag and small sponge, the other holds just a sponge. A small MJ 600 powerhead and a 50watt heater. I have 3 small pieces of LR in there for shelter. Should I have to medicate I will take them out. I also made a plexiglass tank divider should I have 2 fish that may need to be separated for territorial issues.