Time travel
When planning an outing with your child (whether to the grocery store or to a special event), encourage your child to talk about it before, during and after. For example, on the way to the store ask: Do you know why we are going to the store? Yes! We're going to buy things to make a birthday cake. At the store: Do we need candles? Look, here is a pretty cake! Let's put it in the grocery cart. At home: Look at all the things we bought at the store! We found your favorite ice cream. I paid for the groceries with my debit card. 
Use and encourage your child's use of the appropriate verb tense for the time period: future tense for before, present tense for during and past tense for after. The purpose is less about grammar than it is to help your child gain familiarity with time sequence words, the foundation for memory awareness.