Antique Coin

22 fixed on Standard (32 on Insanity), all in the Care Center (on Insanity, 2 in Wrenwood), plus 1 from the roulette and 4 that Chunk drops if you carry the Eye Spy Charm from an earlier run. #1 is on top of the north locker in the Nurses' Station (ch02): climb the trolley before you move it. Each one is in the collectibles list.

Currency for the 4 Parlor cabinets (ch03). Standard: Hip Pouch 3, Stabilizer 4, Steroids 4 and Override Manual 6 (17 in all). Insanity: Hip Pouch 3, Handgun Ammo ×30 5, R.I.P. Knife 5 and Override Manual 6 (19).

You can feed a cabinet a few coins at a time, without carrying the full price. Leftovers become Scrap (5 coins → 1 Scrap) with the Crafting Recipes - Bottle of Acid/Various recipe (ch14, per IGN).