Ireall would like the water as I forgot to bring it and would not be able to survive without it
I can trade more food but I need a bit more water.  
I do need the water as well, I can  trade more firewood.
No I want need at least two packages of water.  I can give you two packages of food and all my firewood.
Sorr I can give you 1 water only or I would not have enough for myself. 
I can give you more food if you like but I really need the water
It seems we both need the water so If you want 2 water, I would need all the food and firewood as well.
How about this I give you 1 package of  water, 2 packages of food, and 3 packages of Firewood.  You get the majority of my items
I guess that could work and seems pretty fair for all.
Ok sounds like deal then.