Sometimes fullscreen apps like Lunia and VLC player wont displa over top of my taskbar, systray, and clock. I want to try and use a bang command to hide the taskbar, but I dont know of any that work.

It depends on the theme as to whether or not it will be easy. Personally I would go through the theme and try setting all of the modules to not always be on top and work on those problems rather than trying to find all the bangs you need to get everything hidden and shown properly. Unfortunately not all themers are nice enough to do things like that for you.

Use the !toggleModules bang - bind it to a hotkey for ease of use.

Set "LSAutoHideModules TRUE" in your personal.rc.