You could use options string that can be passesd while loading levels.
Passing “Value” under variable named “Variable”:
Reading data in new level (must be performed in blueprint, that derives from GameMode class):
This method is pretty limited as passing around complex structures involves serializing and deserializing it from string. Also, passing object references isn’t possible I think. For such cases, storing data temporary seems like better choice, tho I find it pretty ugly. 