Mine for a long time was to simply to buy a cup of coffee.
Of course as soon as the idea entered my head I drowned in pre-thoughts long before I even was with-in a thousand million miles of a coffee shop (yes, ok i "may have, may have exaggerated a wee bit)

My pre-thoughts were building stronger the closer i got, hammering me with thoughts of, they wont have what i want, or I will forget what it is i want when they take my order.

Managed to order my long black.
While i waited I had thoughts that they have forgotten my order and im going to stand around looking like an fool... and should they ask me again what i ordered, i'll go blank!

Stupid coffee, should of brought a bottle of water.

Third gear.
Thinking i should i say something.
My mind is not letting up, but how the hell do i walk back up the counter and check if they have taken my order and if i can would they not think im an impatient fool for questioning their ability.

Finally i hear "long black"
Arrrr but my mind hasn't finished with me telling me perhaps someone else has ordered the same thing and i'm cue jumping? Aaraaaarrrrrrrrh!!

Get the dam coffee and make for the door... of course in a calm fashion lol

finally get out
*Holds coffee to the sky lion king style and roars"... "I have coffee ;-)"
Well, ok no cup raising... and certainly no roaring, but you get the picture.