there is a mod that will put so many stacks of food and water into the trade window when ever someone from your group opens a trade. It may be tradedespenser like sugested. Set your summon food and summon water to a hot key and clock them till you have enough for your group.

You should already have this macro set to a hotkey,

/script AcceptGroup();
/script AcceptQuest();
/script AcceptTrade();
/script RetrieveCorpse();
/script RepopMe();

if you hit this key it will hit accept trade on both toons and the trade is done.

Your question is a little hard to understand what you are asking so if this dosen't do it please re read what you wrote and rephrase the question.