You scroll up and down and it shows how many you're holiding / how many are in the pile.
then press 'A' to make the change

just walk up to it until it says 'check water' or 'check firewood/twigs' then press 'a'
and take some out or put some in.
to put water in the barrel you need a bottle which can be found on the beach.

wow! i'm a n00b and even i know that! walk up to the barrel/wood pile and hit (A) then hit
up to add to, or down to take away. then hit (A) to make the change
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hope this helped

Walk up to the wood pile and press A. The bottom number is what you have in your bag pack
and the top number is what you have in the pile. Press the up button to take the wood out
of your bag and than press A again. If you want to take a twig out of the pile press A
infront of it and press the down button until you have the selected number you want. Than
again press A and you will have that number in your bag.

To put water in the barrel, you first must have a water bottle. Everytime you get a drink
of water, you will also fill up the bottle. You than have to options. You can A) take the
bottle around the island with you and drink out of it. Or B) you can take the bottle to
the barrel. The directions are than the same as the wood pile. One bottle is equal to one
liter of water. You can collect more bottles and fill them all up at the same time and
fill the barrel up quicker.

Hope that helps :]

If you need anymore info just contact me. Or you can look up
my answers on other questions :]

hi i've got a problem here
i accidentally(?) gave the bottle to Skye..
and i don't think you can get anything back from what u gave her...
and the bottle doesn't seem to appear again on the beach..
are there any possible solutions?

When you next get hungry, tell her your ready to eat. There should be a button that leads
to her items. Click it. You can then take any items from her that you accidentally gave to
her. The bottles will also re-appear on the beach and in other places if you just give
them a day or two in the game, not real time.

i agree with emogir0 but the butten u press is x then it should lead to her pink backpack
thing then just press a wile selecting the bottle