PDA

This is the part people miss for whole playthroughs. It works from your inventory, from a Void Bag, or parked in a social slot, so carrying it costs you nothing. The only thing you give up by not equipping it properly is the modifier, which is meaningless on an informational item. In a drunk world it can even show up before Skeletron is dead.

Depth and horizontal position make retracing a mining route trivial, and they are how you find your way back to a vein you abandoned. The rare creature warning catches critters you would otherwise walk straight past. Fishing power tells you whether your rod, bait and the weather are pulling together before you waste an hour on a bad setup. The damage counter is the honest way to compare two weapons instead of guessing from the numbers on the tooltip.

Everything it shows is shared with teammates standing near you, so one person carrying it covers the group. Fold it into a Cell Phone as soon as the other half of the recipe is available, since that stuffs a recall into the same item and frees your hotbar.