When I started teaching sometimes I would arrive at the lecture to find that I left behind something I needed (chalk!, laser pointer, computer connector, textbook, notes, ...).
Do I go back to my office and get it and start the lecture late, or do without?
Sometimes these are things that should be in the room but are not. (e.g. chalk, erasers, or markers).
Even worse was to discover I was missing something in the middle of the lecture!
I eventually came up with a simple solution. Have a separate bag in which I store absolutely everything I need or may need (white board markers, eraser, Mac adapters, text, clicker receiver, course profile, ....)
When I leave for the lecture I don't have to remember or find all these things.
For things like Mac adapters I have an extra one just for the bag.
It is a simple thing but it does reduce anxiety and problems.