[annapurna]

I'll defend Delta to a small extent. We typically don't fly on medical trips in coach but we've never had problems with getting the correct meal up front. I'd make sure to check in a day ahead to make sure the order is there and check with the gate agent again when you arrive. They'll bluster and say there is nothing they can do but when you explain the medical need, they should be willing to make sure that the order is on the flight attendant's paperwork. They may still miss the food but at least you've done all you can do.

We've brought food on every trip and never had security even look twice; except for cheese blocks. For some reason, they look suspicious on x-rays. Other than that, I wouldn't mention your food and be prepared to explain if they ask.

Added thought after the fact: Pastes also gives Security problems. A peanut butter and jelly sandwich probably works; bringing peanut butter and jelly to make one on the flight almost definitely will not work.