In my MM coin box I found last year that I have bought twice (and not at the same time but probably a year apart) electronic parts to make a mod for.. I think they're almost 10 years in there now. Even forgot what mod I was going to make, remembered only much later (light all catapult items when a ball gets ejected)

My Bally Bumper is waiting for restoration for about 7 years now. It's just a long delayed process.
Stripped the playfield 5 years ago. Then didn't proceed when I couldn't find the parts anymore. Found them a year later in my tumbler. Forgot about that again.
A year or 3 ago wanted to continue and again didn't find the parts but remembered they were somewhere in a special place.
A few months ago I found back the metal parts in my tumbler. Last month finally brought the broken lockdown bar to a woodworking guy to have it remade. Once that is back I have all parts to start the restore.

Those are the 2 main I can remember. I'm sure when I look in the coin boxes of my machines I'll find more items I bought with the intention to do someday..
like a spare SC ropelight is waiting 2 years for installation..