Situations vary, but you should always be thinking about worst case,or at least bad case, scenarios and what you would want to have handy to deal with those situations. Right now I am working in the local county elections office - recruiting and training poll workers for the upcoming event. As the election draws closer, job demands could keep me up a great part of the night, or even all night. I keep a supply of food available, both in my desk and in my briefcase, along with a razor, soap, etc (fortunately we have showers available). Pretty soon I will give up bike commuting and drive a car, stocking it with a sleeping bag and at least one change of clothing. It can get pretty crazy and one needs to be able to roll with the punches.

Years ago, when I was making regular trips to the Channel Islands, it was routine to bring at least one extra day's rations. All kinds of events would mess up our schedules and you darn well had to be flexible.