The diner is where the director worked.
It was planned that the director was to make a cameo appearance as the police officer that barged into the diner. Before he could get into costume, the director cut his thumb so the part went to the assistant director while the director shouted from the bathroom.
In earlier drafts of the scripts, the original setting was an airport terminal. Ted Harper was mean to be death instead of part of John's mind. As well the drafts included John and Morgan's child that John kills after he kills his wife. This had to be written out.
The hoodie Dave wears outside belongs to a good friend of the director's, Mitchell Rouble. He added it in there as a bonus.