Firstly, don't panic.
Once you get to the States, getting gluten free and low carb food should not be a problem. Everyone in America seems to be allergic to something so there's masses of food that complies with specific diets or whatever.
With your insulin injections, the time difference will be an issue so you will need to work around this. Are you on a basal-bolus system, or a mix insulin?
If it's basal-bolus, this can be quite easy. You bolus as normal for your food. Your basal, you need to move - if you usually do your basal at 10pm UK time, for instance, this could be something like 6pm US time or whatever, which may not be convenient.
Moving your basal is easy though. You simply move it each day by 2-hourly intervals either forward or back to where you want it to be. So say you usually inject at 10pm UK (6pm US?). Before you go, you might then do an jab at 12am UK (8pm) US and then when you arrive, inject at 10pm US (2am UK). And reverse the process when you go home. Or, you might find that you don't even need to move your basal. The important thing is that if you're on once a day basal, keep 22-26 hours between each dose, and if it's twice-a-day basal, 10-14 hours between each dose.
If you're on mix insulin, you've a little less flexibility in that you will also need to move your meal times forward or backwards. You would move it in the same way you would move a basal dose, but remember to eat after doing your injection.
On the flight itself, you will find that the stress of travelling combined with sitting still for 8 hours will affect your blood sugar. I find that flying just pushes my insulin resistance right up and I need to take quite a bit more insulin on the journey....although sometimes, just to keep me on my toes, I find it's the complete opposite and I need to guzzle regular soft drinks for the whole journey. In other words, expect the unexpected and prepare accordingly. Biscuits are a very good idea. An 8-hour flight will probably also include free soft drinks so you can also use these without dipping into your 'stash'. Test frequently, keep an eye on how you're doing.
And of course, don't forget all the usual rules - keep your diabetes stuff in your hand luggage, NEVER check it into the hold. Don't book the 'diabetic' meal as frequently it is completely inadequate and often can be far higher in carbs than the regular meal.
Also, rest assured that the US is probably the easiest place in the world to have diabetes. You will be astounded by the range of diet soft drinks and the sheer choice of food options so you will be able to find something that fits for you. The hardest part is the portion control!
