I'm thinking I should keep a firm tight grip on the unpurchased merchandise as I leave the store.
So you're planning on stealing from the store? You should go through line and pay instead.
I have to, don't I?
You shouldn't steal things from stores. You could be caught and arrested for starters. It's better to pay for things.
It's fine as long as I get away with it and don't get caught.
It's unlikely that you won't get caught, but if you do get away the store will lose out on profiting from what you steal. They'll jack up the prices to cover the loss, and the rest of us will pay for your crime. Please just pay or come back when you have enough money.