Whenever I take my three year old daughter to the store, she always points to things and says, "Can I have that on my birthday?"
"Yes! You can have that on your birthday," I reply.
She knows that we don't have food like that at our house unless it's someone's birthday. This simple lifestyle change has really improved my grocery shopping experience with my kids. No more being pestered for junk food. No more giving in. And no more junk food in the cart!
The best part is I get to answer "yes" to what she's asking me and that makes us both happy.