What do you do about snacks?
Snacks are a good, practical way of learning a little about the shape of insulin, the way it operates over, generally speaking, say 4 to 5 hours with a peak after say 1.5 to 2 hours (depends on the insulin, and the person etc. but let's use those timings as an example).
So, say you've had lunch, you've carefully counted the carbs, carefully adjusted insulin for carb count/anticpated exercise later in the day/after-drop from previous exercise/ correction for how low or high you are etc. etc.
But because of the number of variables going on which you cannot measure, and the randomness of T1, you're never going to get that right all the time. None of us do.
So, you might find that you start dropping more than expected mid/late afternoon because that lunch bolus is still working for up to 4 or 5 hours. After the event, the drop has made you realise the bolus was too large. In a loose sense, it's gone "wrong" on that occasion, you might rethink it for next time, but I think the more practical way of looking at it is to say, ok, tried my best, can't get it right all the time, now have a slow slide, need to fix that, soo....snack time.
In such situations, if it's a slow slide towards a hypo, not a full on hypo, you'd be well justified in having a small snack, say 10 to 15g, to tweak it back up, eg couple of small biscuits. If it's a proper hypo, obviously treat as accords.
Snacks can fit in quite well as part of dealing with the unpredictability of timing of insulin.
I'm quite partial to a couple of biscuits a few hours after a meal, so sometimes I'll deliberately have slightly more with the lunch or tea bolus to account for that, knowing it'll be peaking 2 hours later, so allows me a snack with peak insulin without having to bolus again for the snack. It's all a bit of a balancing act.
If you're fine between meals, generally snack under 10g doesn't need another shot, but over 10 may, and the higher above 10g you get, the more likely it gets. I'd definitely bolus for a bag of crisps, assuming there's no heavy drop setting in from the previous bolus. None of this is set in stone - it is influenced too much by the other factors relating to that particular moment - so you'll need to make judgment calls for each occassion.
Recently bought a box of the new dark chocolate Digestive Thins, a new take on digestives - 4g each. Will have to do some snack experiments with those...