Alternative to thinking in the future about rewards is focusing on immediate costs. My consumption and enjoyment of junk food has plummeted ever since I went from 'this is bad for me but delicious' to 'this in fact tastes awful and my stomach hurts.' Obviously, this doesn't work as well with my favorite desserts, but if you improve your taste and your favorite desserts become super expensive/rare you rapidly decrease the amount of temptation you face.