Hello I need a lot of water to survive
I have a lot of water around me I can use. So I can give you a lot of extra.
Ok nice I will give you 3 food if you give me 3 water
OK, that works for me. But I would like a lot of firewood. I like to hunt and cook what I kill.
Ok I will give you 2 firewood 
So I get 3 food and 2 firewood? And you get all of the water?
yes does that sound good to you?
Yes, I am happy with that arrangement. 
Alright so let us finalize
Great, I hope your camping trip goes well!🙂