In the script editor, along the left look for and then click on Game_Temp
You want to add a section among all those attr_accessor bits,
That makes a section in game_temp called fight_only, and since you now have a section of memory put aside for your flag, you can set it to true/false.
One other thing you might like to do, is when you first make Game_Temp, you would like the fight_only to default to false.
If (while in Game_Temp) you scroll down to
just after that line insert
@fight_only = false
it will default your flag to false
Just be careful with that bug Atoa mentioned though, it causes a lot of grief....