I don't know the best way to handle it in public, but we always clearly state that a tantrum will not get them what they want and they will have to calm down fi

I don't know the best way to handle it in public, but we always clearly state that a tantrum will not get them what they want and they will have to calm down first. We will also put them in their room for a timeout until they calm down. But I have also noticed that tantrums are highly correlated with lack of sleep. Which makes sense. Even as adults, we are much more likely to lose control and snap if we are less rested and/or stressed. This is why so many parents religiously stick to a pretty structured sleep schedule.