have you ever paid no money but get the goods or service?

I have once. I was 12 that day and would like to buy an apple. I told my dad that I want buy the apple. My dad wants to hurry but he ask me to go and go back faster. So I run to the small shop and get one. I went to the counter with crowded customers. I look at my dad who can't wait for more minutes. So I don't want my dad to angry at me, so I leave the counter and go back to my dad. When we start to leave, my dad asked me about how much the apple is. My God, I forgot to put back the apple!