One of my ex colleagues and friends was sacked for similar.
7hr30 flight packed, non stop demand for drinks...a few glasses of water for themselves...rushed meal...you know how it is.
One of the crew asked him can I take a coke for the room and my friend agreed. They had worked so hard, he felt it was deserved...
Lo and behold, another crew member reports it and that was that!
...but on a happy ending note I am delighted to say the person in question is now with a great airline enjoying the sunshine!!!
Yes it is theft, but on this iccasio nI fewel the company were a bit harsh!