Get some mana or soilent, stuff like that.
You need to eat it before your journey as your bowels need to adapt, once it is good you will have one poop per week as there is not a lot of fibers in it.
It is cheap also. You got everything you need to be well.
There should be a time when the restaurant close for new orders, a time when customers are send out of the restaurant and a time when the employees leave at the end of their shift when everything is cleaned.
If the restaurant is scheduling everything badly then this is not your fault for becoming late. They could have refused the order and decide to take it.
This is their problem.