I would like to give you more food and firewood so that I can have more of the water. I am someone who gets very thirsty very quickly. I'm also a bit bigger than a lot of people and I sweat more as a result. 🙂
that is unfortunate, its quite hot here especially during the day, so I need all the water I can get
I understand that and sympathize. It's very humid and hot here as well. Does it get cold at night there? If so, the firewood would be very beneficial to you. 
its very cold at night, I can have all the wood and give you the food
I would be okay with giving you two firewood but I need at least a little firewood for cooking and boiling water. 
I will take two wood, and two water, how is that?
No, I'm not interested in that because I really need the water. The food I'm okay with parting with more than the water. 
I really need the water too.  its also my most valued item
It's mine as well. Since you need more firewood than I do I would be willing to give you two firewood, one water and two food.
in that case I can take three wood and one water to be fair
I think if you're getting two firewood and two food that you are still making out better on this deal even if you only get one water.
I have given up two of my most valuable items, you should be willing to sacrifice a little too, so its either I get three wood or two waters, and two foods
I won't be cold at night like you will though so the firewood is more important to you than it is to me. I still need at least one firewood to cook with but I'm willing to give that up. I will give you three firewood, one water and two foods. 
sounds fair