well meaning the question is most usefull and not one i couldn't live without. i would have to go with the whip

The most useful thing in runescape?

 

My password.

 

Without it I cannot log into runescape.

Bank, you only got an inventory to store everthing in, you need a bank no matter what. :P

Inventory space, or an Internet connection.

food

Tip It skill, quest, and treasure trail guides

Forging friendship with other people that are very far from you, that without RS there's almost no chance of talking to them in the first place.

Being able to put items in your bank instead of just coins.

For a skill can't decide whether it would be hunting (very good money) or farming + herblore (good profit plus if potions don't sell you can grow and make them yourselves)

 

 

 

For item the most useful would be Runescape runes of course , many people can't be without them , fast travelling and all :

sumoning without a doubt cause then i wouldnt have a helper with me to fight along my side carry things and talk to for funny conversation.