Joseph,
you posted:
What are the circumstances that prevent both a minyan and hat/jacket?
recently the minyon that I doven by was short 2 people. I went outside and to flag down those driving by. With help from HaShem, I managed to get two people to join us. These men were not expecting to be part of a minyon at that time, but they came in and helped us. One of the men did not have his hat with him. This was not the first time that this situation has happened. This is an example of a circumstance for you.