I like flint arrows. I'm not technically hoarding them, I just find a lot of them, so I keep them. And I ALWAYS need wood. So I plant a new tree every time I fell one. That's why I need beech seeds.
Troll leather, I farm troll leather till everything's up to level 3. Technically I don't need it anymore then. So I really don't farm it after that. I just have a reserve for... you know, just in case. ;)
Same goes for root armor.

And yeah, I TOTALLY forgot coal and surtling cores. Although coal comes from wood, so technically I do not need to hoard it, since I can produce it.

Surtling cores, absolutely need to hoard them.