Most useful items, plural.
I really think it depends on the skill
Yeah, but if you really had to think of ONE item that is the most important, besides coins to buy everything, since coins themselves are useless. I'm still thinking of one myself.
You should make a most useful inventory That'd be fun for people to construct their 28 items that they must play the rest of rs with. I'm sure you could make a decent list, naturally neglecting some skills.
Tinderbox -> Hatchet -> Glory ammy -> Mining pick -> Hammer -> 4 Box traps -> Bow
You get the idea.