I have trouble with nude food as we definitely need to use ice packs here in Brissy. I can manage it with a sandwich and yoghurt with a piece of fruit but I haven't figured out how to fit an ice pack with a nude roll - so rolls are always wrapped. For sandwiches a Tupperware sandwich keeper in a soft lunch box fits well with yoghurt and the fruit separate - they eat that first anyway at fruit break which is before morning tea. If you don't need an ice pack in Melbourne it would probably be easier although in Feb you might need one.