If I go long distance or crossings, I have a GPS in an elbow strap, quite similar to the ones runners use for their mobile phones, just a bit thicker.
Not waterproof, but if needed you can put the "carbs" in a thin plastic bag, takes no time to tear open if needed.
But a Yankie or Mars bar or similar, IS in a waterproof packing, so I just stick one of them into the armband, can not be easier, and it IS just for emergency.
I dont know about this one, but just for illustration what, or something similar, could work easy:
I am very careful not having rapid insuline in my body for some hours before going out, based on experience, have had type1 for 45 years.