What do you need? Many work 24 on, 48 off. Many firefighters cook. Some don't work that schedule or cook. So fit your needs to the story.
Keep in mind that some small departments might roll on a dozen calls in a day, with several hours of downtime between. Other departments, like Boston, Chicago and other large cities, are pretty much on scene or on the way to one for 95% of their shift. Some departments may see a fire every two years and the rest are medical calls or traffic accident cleanups. Others see multi-alarm fires nearly every shift they're on.
Firefighters cook things that can be left sitting if they need to run. You haven't lived until you've tried to choke down lasagna that's been reheated eight times in two days and you're taking the first bite. Sandwiches, cereal, eggs, toast, peanut butter, instant rice or potatoes, frozen chicken nuggets and the like are common fare. Almost every agency has a grocery list for the stations, call your local fire department and see what theirs is.
Jeff