Of the 3 mentioned. The one I would recommend the most is Live Rock. Only because the rock tends to bring bacteria which will break down the nasty fish poop.
You can live without a UV and a skimmer for a FO system as long as you stay on top of your water changes.
Fish only systems do not require much maintenance as compared to a reef system. If you ever decide to go reef, then thats where you want to put more emphasis into getting equipment like skimmers, uv, lighting (T5/PC/MH) reactors etc.
FO just keep it simple. LR to act as a filter, a wet/dry to remove some of the poop and you can put your filtation media in there, or a Hang on filter like an Aqua Clear.
Probably throw in a power head or two to make sure you have adequate aeration.
Thats about it.