I did my first half a couple of years ago. Only got up to 16km once in training, so don’t fret about training at full distance.
Do a practice day a few weeks before, to try out how much before the race you need breakfast etc.
I try for 2 – 3 hours before race start, and have a cereal bar in my pocket in the hour before the race and just take little nibbles to settle my stomach/provide re-assurance, normally I don’t eat it all.
Take a gel or two with you, maybe have one at an hour or so, and then one 20 mins later. Probably don’t need it, but it helps my head think that I will have some left for the last couple of miles. Train with gels to see what suits you.
For my first I walked through the aid station at 6 miles, to take a sip or two of water (goes up my nose if I try to drink whilst running) I’ll never be at the front so a few seconds here is fine.
I’ve also taken a bottle in a waist belt, which worked as I didn’t need to slow down to drink.
All been 1:50 or less using this strategy, and I didn’t start running until my late forties!
Oh….have a poo before you leave home or stop on the way…the bogs are always queued out of the door at the venue, and you don’t need that stress that close to start time.