Hmm, tricky one this. Sandwiches would be fine but I know when I've done night shifts (esp the first one) I am starving by 2am. Take something like a mug shot which you could make if you wanted to and lots of fruit.
If you have to do more in the future, you will get a feel for what you would like to eat and how hungry you are and you may find leftovers to microwave are good.
Is it tonight?