As it is also nice to encourage homebrew and mods, test equipment is a great idea.
I still use the Elsie inductance and capacitance meter, the one that reads in morse, that was kitted by njqrp. Let's see if could be used as frequency counter. A two level signal generator like norcal once kitted. I have the 4state test set, and I used it to sort xtals and its audio generator.
While I enjoyed copying an ozark patrol, I also did a WBR regen, its amazing on cw, don't think its ever been kitted. It is a huge upgrade over simpler regens.
The agc I placed in my ubitx, using a bright led and photoresistor is amazing. It would benefit any receiver without agc. Hasn't been kitted that I know of.