Many many regrets, the list is long. Probably the one I think about the most is a Martini Cadet that we made into a .218 Bee in high school auto shop in 1961 followed by a S&W Mod 53 complete with inserts.

How about a pre WW2 Win 70 Super? in 375 H&H that I bought off Amand Swenson (Gunsmith from Washington - 45 Auto parts- built race boats for Oley Bardal) that was so old that he had to drill the scope mount holes in it for me. I traded a GI 1911 and Pachmayer pistol box for it. Its most likely somebodies 450 Ackley Mag. now. Or what about a blued factory fished(like a Mod 29) S&W Mod 1917 45ACp marked "U.S. Navy" in 99% condition. Had to sell both to make rent just after I got married in 1970.

It usually take a while to sink in but it hits harder and harder as time goes on.
Savage 99 30-30 carbine
Savage 99 250-3000
Sako 72 22lr
Sako Forester 220 Swift
(2) Beretta 76 22 target specials
pre-war 270
pre-war 300 Ackley Imp
pre-64 243 fwt
pre-64 308 fwt
(2) pre-64 30-06 fwt
There's more but I think of these often!!

A Ruger Single Six Magnum 32 H&R. Bought it for $185 in the mid 90's.