Egads I've just wandered into the thirtysomething forum!
I regret not keeping my full Micronauts, G.I. Joe, and Matchbox car sets. I also mourn the Chainmail D&D, AD&D, and Traveller complete rules I gave away. Met these writers, Eastman and Laird. They signed and gave me an early print of something they called Teenage Mutant Ninja Turtles. I traded later for a mint copy of Frank Miller's The Dark Knight Returns (signed) sold it for $50.00. I do not regret, however, giving these things away and moving on to bikes and girls.
I miss my first bike. It was stolen the first time I ever snuck away to meet my first gf at the mall. I guess that first kiss made up for it.
I still miss the bike more than her. It was my first ten-speed, I felt like a badass.