Here are some of the things you will find:
Sticks to absolutely everything: you, the floor, your enemies.
When spilled, oil turns into slippery slicks, causing everyone to slide across. But when ignited it can make for an effective patent BBQ.
Storing explosives in barrels and leaving them to stand around in hallways is a time-honored tradition. You're perhaps best off not using these as cover.
Like explosives, but with the added fun of freezing in place everyone it doesn't outright kill.
Acid is all around you: in barrels, in jars, dripping from the ceiling. It sticks around too, so be careful.
Wombat Blood & Horse Meat
Delicious foodstuffs for everyone. Found in barrels and fridges. Great for restoring your hit points if you're this sort of thing.
Fire hot. Fire burn. Fire ignite.
It's not really clear how this stuff works, but a few splashes, and you feel fantastic and nigh-invulnerable. Same goes for your enemies, so it's best you don't let them bathe in the stuff.
Quite the opposite of the above; results in terrible hangover-like symptoms like decreased speed and increased vulnerability to damage, especially of the unholy kind.
These creatures are less than pleased about being stuck in a jar, and will make their displeasure know to whoever's nearest as soon as they get out.
Sparking with unholy energy, these books whisper of their dark and (of course) Lovecraftian contents. Disturbing their slumber tends to cause violent explosions.
Tables, Shelves, Beds, etc.
This stuff is just in the way. Ideally in the way of enemy shots. You can climb up the side of anything by pressing against it and moving up at the same time - so to climb a table on your right, press D and W, or right arrow and up arrow.