I copied the link that Ricardo gave. I was so excited that the answer was from Amy Waterman.
Voy a la tienda is correct if you want to say, "I'm going to the store." Use ir to talk about movement in a direction or when you have a destination.
Use "me voy" when you're talking about leaving or going away. For example...
_We're going, bye! _ ¡Nos vamos, chao!
_I'm tired, I'm going. _ Estoy cansada, me voy........Amy Waterman 2006
I guess I can add "Me voy a celebrar", "Me voy a bailar", Me voy a cantar", "Me voy a estudiar". "Me voy a comer or beber or any verb I guess.....Aurora 2014