Well, in 1994 when I picked up the Russian SKS for $75 out of the crate I got to pick from, I should have bought the 10 full crates instead.

Even though I wasn't really interested in them back then, I should've also made it a point to buy at least one Colt Single Action Army each year and just stored them away. There's a saying that Colt SAA's and an ounce of gold are worth about the same. That holds historically pretty much true, with gold being more finicky. Depending on caliber and other features, some Colt's far outpace the gold.

And something full auto.... when I had a chance to buy the .380 MAC for $3k, the Uzi for $6k and the full auto AR for $12k, I should've found a way to make it happen...

Full auto sooner
A few more non-rail SIGs
77/22
New S&W 27 and 29 revolvers

I'd still have a P220 and P226 in every caliber, but would have bought a few full custom pistols sooner (too bad I still wouldn't have been able to afford them).

Browning BDAs in all the calibers.

I know this is the pistol forum but also...

100 AK parts kits w/barrels - bulk price @$40

500 new 20 round Hungarian AK mags @$6