I've been reading some "advice" on eating whilst on shift and to be honest, there is a load of crap.
For a start, one suggestion is to "maintain your regular meal times". Load of baloney. If you get out of bed at 2pm, eat lunch, have dinner at six and then work a whole 12 hour shift on an empty stomch you'll either a) get huge cravings and end up eating lots of crappy foods or b) fall asleep halfway through the shift. Plus eating breakfast and then going straight to bed is surefire disaster - you'll upset your sleep and very possibly end up with indigestion. Any sugars and fats ingested get little opportunity to burn off so you'll also end up putting on weight.
My suggestion is to maintain eating hours as if you were working during the day. For example, eat something as soon as you wake up, and don't eat less than 4 hours before bedtime. Here's my suggestion for a 12 hours shift working 7 to 7:
Wake up time 3-4pm
Eat a "lunch" light meal within 1-2 hours
Have dinner between 10 and 12 pm
User your lunch break for exercise (burns off the fat and ups the metabolism for the rest of the night, will help you stay awake)
Have breakfast between 2.30 and 3.30 pm.
Finish at 7am - bed between 7:30 and 8am.
Sleeping patterns. I work around jet lag style complaints by sleeping an extra 2-3 hours the morning before starting a night shift, and then add a little extra sleep for the next couple of days to compensate for the time lost. At the end of the shift I cut my sleep by 3 hours and add extra time accross the next couple of nights - otherwise you'll find it very difficult to sleep when readjusting to a daytime schedule.
Avoid the vending machine like the plague. Carry no change so you cannot be tempted.
Drink plenty of water throughout the shift.
Avoid late night canteens unless you work in a factory or office where there is a large body of night workers. Otherwise the food will probably be complete rubbish. Try to stick to light and easily digestible foods.
I find wholegrains an excellent source of nighttime carbs as they digest slowly and give you the extra energy you need later in the shift.
Emphasize fruit and veg. 3 pieces of fruit before each meal is good and include at least 1 veg with the two main meals.
Don't drink caffeine laden drinks after breakfast or you won't sleep. (Strangely enough I come from a family where drinking coffee at 11pm is quite normal and we're all night owls).
Don't let there be more than a 6 hour gap between meals or the cravings will kick in.
Take a multivitamin every day - it helps.