Beer. Don’t think I could ice fish without it.
Been thru different locators, rods, augers, houses, atv’s over the past 20 years but have almost always had beer with me on the ice.
But on a more serious note, I think the single most productive lure for me is a variety of sizes and colors of Custom Jigs & Spoons Demon lures. Smaller options for panfish and perch, and larger variations for walleye, pike and trout.