I will use something other than food for the directions, to avoid the issues with allergies.
Some students could write instructions to a specific part of the school and have another student follow them, taking a photo of where the instructions really sent them. I'd probably have simultaneous, in-class activity so that I don't have a whole class in the halls at the same time. Students could then revise their instructions, based on results.
The type of instructions could vary for different groups within the class: some giving directions for a place in the school, others give directions for drawing a picture without seeing it, others for creating things from Legos, for example.
I also like the idea of modifying instructions, as listed by @jkim.