Hi
@Jayden2407
Firstly, I'm not the parent of a child with diabetes, but my son does have ASD, so I can relate a little to the anxiety you feel about going away to a strange place with a child with additional needs.
Here's my take on it. Whether he had diabetes or not, you'd be watching him like a hawk, making sure he stays safe and has fun. It's a family holiday after all. Given that you'd already be watching him, that he's not expecting to spend time away from you and that you say he's "not keen to advertise his diabetes", I'd say not to ID him with a band or whatever.
What I used to do, when out and about in busy places with my son, would be to write my mobile number directly onto his arm, just above the wrist. Not in huge numbers, but large enough to be seen clearly. And then I'd rehearse with him who he needed to talk to if he couldn't see me anymore (people in uniforms belonging to the place where we were; people marked "steward", emergency services people, people with small children failing all of those).
I always felt that by identifying him by his disability, I was making him more vulnerable in a way, and in a big crowd, the priority was finding the lost boy, not finding the autistic boy, if you see what I mean.
Of course, though, as a parent trying to plan ahead, you also need a back-up plan just in case. And what I'd say is that you have all his medical information and emergency kit with you whenever you go out, but you just find a way to get your mobile number on him. But, honestly, if he wasn't the sort to run off before his diagnosis, he won't have changed much from that. And 10 is old enough to understand the rules of the situation.
I know you're deep in Mummy Mode, and planning this out ahead of time should (I hope!) bring you peace of mind when you go on holiday. But trust your instincts when it comes to your son. Perhaps consider buying him a little pay-as-you-go phone so that he can get hold of you if he needs you and you're, I dunno, in a swimming pool changing room or the loo at a restaurant.
Honestly, I'd say write your mobile number on him, rehearse what he needs to do in an emergency (of any kind, not just a diabetic one) and then trust him.
And, of course, have a FAB holiday!