$5 12pt / 3xSq / XZN socket set
 

For those who do wrenching on European cars and don't have a set of triple square / ZNX / 12 pt handy. Summit Tools has a 3/8" drive SAE or Metric sets for $5. It is Allen brand (as in Allen Wrench but apparently it is part of NAPA). The Metric is 9 pieces from 10mm - 18mm.

For people who don't know, they are usually used in calipers / doors etc. Chances are you will use it once every 5 years.. but $5 is a good addition to your socket drawer.