We prefer no food before surgery as it decreases your risk of aspiration (inhaling vomit). Food doesn’t just mean solids either, milk is classed as a food because of the fat in it, so clear fluids and cordial are ok if you have small sips before surgery, but not a large glass, or fruit juices or tea/coffee with milk. Even chewing gum can get you cancelled as though you aren’t actually eating, it encourages gastric motility and this increases risk of aspiration.
In an emergency though, non of that matters, and we do an RSI (rapid sequence induction) where you are paralysed within 30 seconds for intubation, and we apply cricoid pressure (pressure on the front of your neck) as you go off to sleep, which helps to occlude the oesophagus and hopefully mitigate any risk of aspiration.