Yeah this is called "The path not chosen" (or something) and it is a recognised facet of human personality.
You spend half the night wondering something like "I should've opened with sponges instead of cards" when in fact had you have started with sponges you would be thinking quite the opposite.
The best thing to do is to not beat yourself up about it. Which is easier said then done.
There is some excellent advice on here; Deshi and Discoman suggest setting a time specifically for this type of thought. This is good and usually works for me.
The second is to 'bookmark' the end of this thought-time by doing something completely different - a nice soak perhaps.
Lastly, it helps me to remember that I got the job done, and I did it very well. Despite all of the little things that I feel I could've changed, people were suitably pleased and entertained (and probably wouldn't have noticed anyway

).
