A simple file saving class for Unity (or really any C# project if you drop the inheriting from MonoBehaviour).

Saver.cs

// File saving.
// The data being stored should already be serialised somehow.
// Obfuscation is not in the realm of this class either.

using UnityEngine;
using System;
using System.IO;
using System.IO.Compression;


namespace NSC
{
	public class Saver : MonoBehaviour
	{
		// Convenience function to save strings. Saves precious seconds of typing.
		public static bool SaveData(string filename, string data, bool compress = true)
		{
			return SaveData(filename, System.Text.Encoding.ASCII.GetBytes(data), compress);
		}


		// Save as gzip-compatible files. Can be decompressed with command line gzip as it has a header.
		// Returns true if saving went well.
		public static bool SaveData(string filename, byte[] data, bool compress = true)
		{
			if(data == null || data.Length == 0) return false;

			FileStream file = new FileStream(Application.persistentDataPath + "/" + filename, FileMode.Create);
			if(file == null) return false;

			if(compress)
			{
				GZipStream gz = new GZipStream(file, CompressionMode.Compress);
				if(gz == null) return false;

				gz.Write(data, 0, data.Length);
				gz.Close();
			} else
			{
				file.Write(data, 0, data.Length);
			}
			file.Close();
			return true;
		}


		// Loads a file into an array, decompressing it if it's in gzip format.
		public static byte[] LoadData(string filename)
		{
			byte[] data = null;
			FileStream file = new FileStream(Application.persistentDataPath + "/" + filename, FileMode.Open);
			if(file == null) return null;

			GZipStream gz = null;
			BinaryReader br = null;

			byte[] header = new byte[3];
			file.Read(header, 0, 3);
			file.Position = 0;
			long realsize = file.Length;
			// Inspect the header for the magic numbers gzip files start with
			if(header[0] == 0x1f && header[1] == 0x8b && header[2] == 8)
			{
				// It's gzip, so the 5th to 8th byte are the size.
				// Yes, that's a 32-bit number, so file size is limited to around 2GB uncompressed.
				byte[] x = new byte[4];
				file.Seek(-4, SeekOrigin.End);
				file.Read(x, 0, 4);
				file.Seek(0, SeekOrigin.Begin);
				realsize = BitConverter.ToInt32(x, 0);
				gz = new GZipStream(file, CompressionMode.Decompress);
				br = new BinaryReader(gz);
			} else
			{
				// Not compressed, read it raw
				br = new BinaryReader(file);
			}
			if(br == null) return null;

			data = br.ReadBytes((int)realsize);
			br.Close();
			if(gz != null) gz.Close();
			file.Close();
			return data;
		}
	}
}

SaveTesting.cs

// Class to test that saving/compression works in Unity.
// Largely untested outside of OS X.

using UnityEngine;
using NSC;


public class SaveTesting : MonoBehaviour
{
	void Start()
	{
		string s = "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz";
		Debug.Log("Input size: " + s.Length);
		Saver.SaveData("savegame", s);
		byte[] s2 = Saver.LoadData("savegame");
		Debug.Log("Output size: " + s2.Length);
		Debug.Log("Result: " + System.Text.Encoding.ASCII.GetString(s2));
	}
}