Rickle Axager's Pocket Guide to Adventuring, Third Edition

Rickle Axager's Pocket Guide to Adventuring, Third Edition is a compact book which can give Advantage on a skill check.

Description
Once per day, one can read a section on an associated skill check, and for the next 24 hours, have Advantage on it. And one can also read that aloud to give the Advantage to another party member.

Price
The Pocket Guide is widely believed to cost 1500 g, but Taako buys it and The Slicer of T'pire Weir Isles for 2000 total, and The Slicer of T'pire Weir Isles costs 900, so the Pocket Guide must have cost 1100 g.

Episodes

 * Ep. 50: Immediately after buying it, Taako used the Pocket Guide to gain advantage on Persuasion, saying "'cause I figure, there's no need to waste it". He then uses that advantage to trade The Slicer of T'pire Weir Isles to Garfield the Deals Warlock for the Flaming Poisoning Raging Sword Of Doom.