Unless you allow transferring from another world it is impossible.
You need Waffle's Iron & Ocram's Razor, which is exclusive to GFB
GFB doesn't have a contaminator. No way no how.
I tried this myself some time ago, I got about 3000 before stopping, I might still come back to it. If you do try this remember that a lot of item IDs are blank due to reasons I can not be sure of, I would not know. Also, toggleable items like the encumbering stone and most notably the
shellphone are stored as seperate items for their settings, Shellphone (home), Shellphone (spawn), Shellphone (ocean) and Shellphone (hell) are all different item IDs and may need to all be collected depending on what rules you give yourself. There are also the unobtainable items like the lunar axes and hammers, first fractal, the dummy item for the shellphone which doesn't have anything on it's screen, lunatic cultist treasure bag, and even the heart and star pickups are technically items which by all intended means can not be put in chests.
I'll also take the time to clear up some
LIES. You can shimmer vile/viscous powder into purification powder. Badger's hat just requires beating EoC and WoF on the same day, nothing about both being a first time kill, you can just do it in the post-game. You can shimmer every type of hardmode crate into it's pre-hardmode variant, including divine->hallowed crate, you still need a gray zapinator though. Carrot has been discussed above, you can modify your steam version for it and Red has even hinted that he doesn't have a problem with it since CE is well out of circulation now.
Love you all!
Good luck if you plan on trying this, I found it quite fun going through every item ID actually. If organisation is your thing I recommend at least going for the first two chests Item IDs 1-80.