Ever since the children were first weaned, I've always been in the habit of packing a drink and a snack to take along with us. Harry was very easily bored as a toddler, and taking a small box of raisins or Cheerios out and about with us was a good way to keep him occupied if we had to wait around somewhere. But it wasn't until Mia came along that I really understood how necessary it was to keep a snack in my bag.
To be fair I should have been quite familiar with the possibility of 'hangriness' (becoming angry through lack of food or drink) because it's something that Ram suffers with and I'm used to making sure that our trips out and about involve regular snack and drink breaks. Ram will often get even more hangry if I try and get him to eat something, but after he has eaten he'll recognise his hangriness in retrospect. But Mia's hangriness is completely different.
I have discovered that Mia needs to eat regularly, by which I mean every couple of hours, to stop her bad mood from descending into a screaming meltdown. It doesn't need to be much, it can just be something that doesn't feel very filling, like some sticks of pepper or cucumber, but it is enough to stave her off for a short while. I can always tell if she's due for a snack - she won't usually say that she's hungry unless I ask, but there is a noticeable downturn in her mood that can often result in a full on lying on the floor tantrum.
So if we are leaving the house to go somewhere and it's been a couple of hours since the last meal, I always make sure that I offer a small snack before we leave, alongside toilet trips and shoes on. I keep a packet of breadsticks and a water bottle in the car ready for the drive home from school, and I always have a bottle of water as a minimum in my bag, even if we aren't popping out for long.
I don't think that it's an uncommon thing in children (and adults!) so at least I'm aware of it, and most of the time I can prepare appropriately!
Does anyone in your family suffer from hangriness?