That may feel weird to some people (it does to me, for instance), but it's not in the same category of events. You paid for it. Rationally, as long as you know you're good for it, there's nothing massively wrong with it. I say it "feels" weird precisely because I know rationally it isn't wrong, or is so little wrong it doesn't matter much. (I mean, I've been in situations where it turns out I ate at a restaurant but didn't have my wallet, and I had to go make it right. That sort of thing happens. If you really get down to it, yeah, sure, it's wrong, but we can't run a society of human beings if we start bring in the legal system or something for all those things.)

I would also add that if the store owner came up to you and challenged you to please pay for that right now, you're obligated to do so. Considered as a whole, it's not a good idea for someone to do that over a bottle of soda for all kinds of reasons, but I'd say the right still is essentially there.