Sorry, this is long, I'm stuck at home with a knee injury and too much time on my hands!
I've had a pump for almost two decades, and pens for the two decades before that. Use a blood testing device rather than a Libre cause I can't bear the idea of yet another needle in me.
Don't drive a car, but walk, cycle or use public transport.
If a really really short trip, such as 15 minutes walking: just three or four sweets in a pocket or in a ziplock bag in a backpack. Ziplock bag keeps them together, makes them easier to find, protects them from getting bashed about too much, and is easily hauled out as is for transferral to a different bsg
A several hour walk or cycle, backpack and probably about 8 sweets. Usually water as well because if my sugar was/goes high I want to be able to deal with the thirst in a way I can control. Vlood testing kit if very intense exercise.
Full day out, blood testing kit (case containing lancet, blood testing device, 1 tissue, small flat plastic envelope to put used strips in), 8 sweets, water.
Long trip abroad (parents live on the other side of the world, so very long haul). The whole shebang: in my suitcase, spare pump (old one but still works), spare blood testing kit (actually had one stolen out of my bag once - presumably they thought it was a wallet- when on holiday!), extra tissues, full bag of sweets).
In my carry on bag (large backpack): all needles, cartridges, written down record of my hourly basal rates, phone number of the pump company in case of emergency, insulin, disinfectant spray. All that kept in a very large ziplock bag to keep it together, with the insulin and disinfectant in a smaller ziplock bag nestled at the top so its easier to haul out and put back in when you need to show liquids at airport security. Plus of course sweets etc.
Stuff actually needed on the flight, such as sweets and blood testing kit, as well as a book, in yet another ziplock bag so can be hauled out on the flight without having to disrupt any of the rest.
Always with ample spare insulin, needles and cartridges. I was in India when 9/11 happened and was meant to fly out the next day, then all flights were canceled for a week and no idea at the time when flights would resume. Was very glad to have a lot of extra.
Would never carry juice. For me, too heavy what with all the rest one has to carry, and too prone to leakage if badly bashed about. Also, once in a blue moon sugars go low and insist on staying low, so if one only had juice, one would have nothing left to treat the low.
Sweets - don't know if you have these in the UK- but Lidl where I live has soft, fudge consistency sweets (Kleine Kuh or Sahne Muh-Muhs) which are individually wrapped in paper and basically dissolve in your mouth without needing to chew. Polish shops also have similar. Much better than having to chew or crunch something, the paper keeps them clean, and 1 or 2 are usually enough to treat a low.
Back when on a pen, if offered unexpected food between meals, unless already going low I would just thank them and say no.
I like my food, but either going too high or having to take an extra shot would just not be worth it to me. Particularly when the extra shot is likely to mean you still have some active insulin when you reach the next mealtime, just making everything more complicated.
As a complete side note:
I once started a detective story, borrowed from the library, in which the police detectives "realised" a death in what appeared to be an accident was actually murder because the dead man was Type 1, and had a chocolate bar in his pocket at the time of death. They "realised it had been planted there by the murderer, because a Type 1 diabetic would never carry around anything sweet."
I stopped reading at that point. Had it been my own book, it would have gone in the bin.