I plan on uninstalling and reinstalling league to fix some un-relevant issues. However I do not feel like re-applying all my custom video\interface options. I also don't wish to remake my custom item sets for my champions. Which files would I need to save first to keep these custom settings?
C:\Riot Games\League of Legends\Config (installdir\Config)
game.cfg contains the game settings like mousespeed, volume etc. I think this is what you need.
input.ini contains all of the keybind settings that you have changed from the default.
Both can be opened with notepad.
If you are on a Mac (osx) then, go to:
Applications -> League of Legends -> Right-click the icon -> Show Package Content -> Contents -> LOL -> Config
You'll find the following: