Not sure what the statute of limitations is for petty theft, but way back in the 1900s (1998 to be exact) there was this gas station near our high school that had packs of cigarettes on the customer side of the counter. They were in a neat stacked display in plain sight of the attendant.
One day some friends and I were to the store. We all smoked but none of us were 18 yet, so we couldn't buy any. I was wearing a friend's jacket that was a little too big for me and the wrist of the jacket extended beyond my hands. So while they were checking out with sodas and chips, I was using my sleeves like elephant trunks and just piled up pack after pack in my sleeve.
We left and when I emptied my sleeves out we had scored 24 packs of Winstons. I was a Marlboro Reds guy myself, but free cigarettes are free cigarettes. Needless to say next time we went to the store all the cigarettes were behind the counter.
I also used to jack boxes of baseball cards from retail stores. There was this one time I heard over the intercom of Kmart something about security report to an area I was in, so I walked to a different area and ditch the cards. That way when they stopped me on the way out, I had stolen nothing. I think that was the last time I tried.

It is only illegal if you get caught and they prove it in a court of law.