Hey jjones, congrats on taking on the challenge of a half marathon!
Each of is is different, but here is what works best for me.
1. On long runs, I wear an amphipod belt, which holds water and/or gatorade, shot blocks, and my blood glucose meter/strips/lancing device.
2. Cut the basal rate on my pump to 60% of the normal amount an hour before I start running. Keep that same basal rate for the duration of the run, or lately, I've been going back to the normal rate before that.
3. Eat a light breakfast about an hour before I start running and bolus for 50% of the carbs I normally would.
4. Test before I leave; test again after 2-3 miles to see how I'm trending. See if I'm dropping rapidly, or lower than I'm comfortable with and if so, eat 1 or 2 shot blocks. Test again after 5 or 6 miles and eat shot blocks if needed. Usually after that, I can leave it alone and go by feel and based on the knowledge of what my BG trend is like. For me, the key is catching any drop in BG BEFORE it gets too low and requires me to walk or stop and wait it out.
Good luck, and happy training!