This is a common issue- you go shopping with the kids and they get hungry. So you take something off the shelf and pay for it later. The stores in my area don’t have a problem with this. Forgetting about what happened in Hawaii, is this a problem in general? Would there be a difference between Jewish stores and goyishe stores?
I usually have a rule no opening packages until they are paid for. Sometimes, though, my kids get so famished or thirsty that they cry and so, I too, will open a package and pay when I’m done shopping. When the lines in a supermarket are VERY long, I can’t see waiting for 15 minutes to pay for a drink and then return to shop!
I always knew that opening a package before paying for it is against Halacha, except if you get permission from the store owner. I may be wrong though.
I bring along snacks from home to give my kid while I shop.
Why would you not be required to pay for it? It’s shoplifting otherwise. The store clerk can scan the wrapper without the contents – if you get a curious look it would be a kiddush Ha-Shem to explain the kid couldn’t wait to get home to eat it.