You should always have at least 1 of these items on you, as they are used for various actions throughout the game. (and some in multiple side quests)

Rope, (used to climb down things, can sometimes be substituted with jumping for damage)

Prybar, (used to pry open a door in pyrshen, unsure if other uses aside from that)

Grappling Hook, (same as the rope, might be usable in more locations?)

Shovel (used to bury and dig up graves, and for a few sidequests)

These are all of the items I've used to complete sidequests so far. I'll be updating this list as I find more, as well as their quest-end locations. This list isn't complete yet, so feel free to comment if I've missed something.

Something nice about this game is most items can be bought in item shops, so once you know what you need, you can simply buy it rather than waiting for random drops. (and if you can't find an item in one shop, it might be in another)

remember, west is left <
east is right >
south is down v
north is up ^
I always confuse west and east, so a good way to remember is the word "WE" as West is left, and East is right~
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5 blight blossoms (visible plant monsters at various locales that you "talk" at to fight, VERY IMPORTANT, as it's needed for the main story) (worry not, you can buy them as ingredients as well, at the very least from a witch past Durgim's Mill)

20 silver dust (needed to purify a well)
1 silver dagger
1 sapphire, (can be bought from the center pyrshen merchant)
1 ale, (can be bought in taverns) (pyrshen center)
1 lock, (purchased from the armor shop in Vulkoid, east of the main quest commander)
5 paintbrushes, (Pyrshen west)
5 bandages,
1 blank book,
1 rope,
1 prybar (pyrshen east)
1 grapple hook (Pyrshen South)
1 candle,
2 blankets,
3 incense (neerford)
5 swamp truffles
(5 more? swamp truffles to make a pig happy)
1 spear, 1 bow, 1 hand axe(all part of one quest in the south-middle part of the map, at a watchtower)


Repeatable Side Quests:
Bones, Vampire Dust and Wolf Furs