How to save variables between scenes?

I have a thing set up to change the variable up one every time i click it and i need it to save between scenes to put on the score scene and when you go back to the clicking scene for it to not disappear.

I use non-MonoBehaviour singletons or static classes to pass data between scenes.

Simplest: Static classes. Cons: correct initialization can be source of problems sometimes

public static class Data
{
	public static int score;
}

Then you can access it from any scene like so: Data.score = 100

Singletons are a bit better since you can always recreate them if you need to clear all data and start over.

public class Data
{
	// keep constructor private
	private Data()
	{
	}
	
	static private Data _instance;
	static public Data instance
	{
		get 
		{
			if (_instance == null)
				_instance = new Data();
			return _instance;
		}
	}
	
	public int score;
}

This one can also be accessed from any scene like so: Data.instance.score = 100;