At least five days when I was in a feverish hell of mono, just drank a lot of water.

Other than that, I have gone without eating for like 24 hours or so a lot when I was younger either by just being distracted and not being hungry or when I was broke in my early 20s and had to couch surf for a couple of months. Got by eating once a day.

Now my meals are so structured that it would take effort to get back to eating only when hungry but I should start that so I can get back to a healthy weight.