Long interview

Congratulations on your interview.

If they hadn’t told you how long the interview was going to last for, and said turn up at X time, do you think you would be so anxious? The interview might turn out to be less than the 2.5hrs they’ve said. 2.5hrs could be worst case scenario.

Given you’re worried, I’d probably be tempted to eat a large mid day snack/meal before the interview and eat again when it’s over, just in case the format changes and the break doesn't happen.

Based off what you posted above, I would also add that I think you should seek help for your anxiety and issues with food.

Have a proper meal at a location close to the place the interview is at, an hour before the interview is going to start, then, by the time the food arrives and you've eaten, you'll have 20mins or so to get to the interview (or use as "just in case time" if you are virtually next door) and you won't have to eat anything until after it is all over.
If it reassures you though you can stick a couple of cereal bars in your handbag.

First I would check whether they have included a lunch break in the 2.5 hours. It's not impossible that there's a lunch included. We have sometimes had lunch with candidates so other team members can meet them.

Assuming that's not the plan, I would get there early, find somewhere you can have an early lunch at 11am. And also stash some snacks in your handbag so you can ask for a "loo break" and eat them if necessary.

Good luck!

In your situation I'd have a large brunch at 11ish, including eggs and filling foods.

Plus take a cereal bar in handbag for emergency use - so you can pop out to the loo if you're feeling weak or ready to eat immediately you're finished if you don't need it.

Done.

Interviewers normally ask you if they need to make allowances these days don’t they? I’d just tell them I’ll need to eat during that time due to low blood sugar issues.

For the job I'm currently doing I had to do a task in advance (excel spreadsheet), 5 hour team building. And 2 hour in tray exercise / panel interview. We were provided with snacks and lunch. Good luck!

I feel likw that sometimes. I thibk it is low blood sugar. Make sure you have a protein rich meal beforehand and maybe pop a little pack if meat or cheese in your bag and take a liitle bite or two when you pop to the ladies if you feel a bit off.