Much of this post (including its title) was taken from Untimately’s post, http://untimately.blogspot.com/2012/07/od-equipment.html.
I have a few quibbles with it; I prefer my die rolls to select from among equally powerful options while those rules prefer to match OD&D’s starting gold.
I like knowing that your character didn’t bring a gallon of water into the dungeon, but rather brandy.
I like knowing that your gourmand character fries their rations in oil and garlic over the campfire, drawing the attention of gnomes while repelling vampires. Or that they have salt. Or pepper.
I like knowing your herbalist has catnip in their kit, or basil or wolfsbane.
A lot of this is still on the equipment lists for 5e, but notably absent are the bits of gear you carry as a specific countermeasure against specific foes.
A given object can have one or more properties, either by analogy to already existing gear or new properties, below:
Attracts X: creatures matching X desire to attack it or possess it, and so will preferentially attack or harass a character carrying or doused with the substance or object. If a character can manage to rid themselves of all of the substance, it often makes a good bribe for its creature type.
Effects that end on a save are generally only effective once per target per day; reapplication doesn’t do much.
Holy water: 25gp, as oil and then acid vs. fiends and the undead (1d4 radiant damage and +5 radiant damage). The square hit is treated by those foes as containing (radiant) caltrops thereafter.
Salt: 5gp for 1lb, as acid vs. slimy bugs and oozes and fungi (salt damage*). The square hit is treated by those foes as containing (salt) caltrops thereafter.
Blinds undead on contact until/unless the victim succeeds on a DC 11 Wisdom save as a standard action.
Offal: free for 1 lb. Attracts stirges, ghouls, and sharks. As oil but for disease, poison and necrotic damage. Blinds scent until/unless they succeed on a DC 11 Wisdom save as a standard action.
Wolfsbane: 1gp for a sprig. May be wielded as a dagger against wolves, werewolves, hyenas, gnolls, etc (silver and poison damage). Resolve as a pool of lit oil if brought into continuing contact.
Belladonna: 1gp for a bunch. If eaten, acts as antivenin against lycanthropy.
Bezoar: 50gp per. This is the antivenin in the rules.
Honey: 1gp for 1 dose. Attracts insects. Acts as one charge of healer’s kit.
Powdered silver: exactly as holy water.
Powdered iron: 1sp per dose. As flaming oil against fey and incorporeal undead (force damage), including continual contact.
Iron weapons deal their normal damage, but additionally gain the force type.
Garlic: 1cp per dose. As wolfsbane against vampires. Attracts snails and creatures with scent. Often aerosolized via incense, candles or dinner, remaining effective and suffusing the space.
Pepper: 1sp per dose. Blinds scent on a hit until the victim makes a DC 11 Constitution save as a standard action.
Cockerel: 2cp, room and board. Advantage on checks made to hear things while asleep, disadvantage on sneak checks, you’re carrying around a fucking chicken. Basilisks and fiends are Frightened of cockerels unless they succeed on a DC 11 Wisdom save. Attracts predators, especially foxes.
Cat: 2cp, room and board. Can see ghosts and other invisible things with full concealment even if otherwise hidden, though usually too cool to react, and occasionally spazzes out at nothing. Attracts canid monsters and vengeful rodents, avians.
* Why invent my own damage types? The creatures I intended to harm with this effect are resistant to the sane damage types! A damage type off “as X but ignores resistance” is effectively a new damage type anyway.