What piece of equipment do you no longer have that you miss the most?
As a body, I miss my Elan 7e, but overall I used to have a superb copy of an old 100-300 f5.6 L that I miss the most. I sold it to finance a 70-200 f2.8 L IS for my son's high school football, but always resented that lens because of what I gave up.
I eventually sold that, after my son's graduation, and bought another 100-300 f5.6 L, but it's just not the same. 



