This is really easy...and really obvious.
I know everyone is gonna say this is just common sense, but you wouldn't believe the number of people i've been grouped with that say: "i gotta go buy some food first" instead of using this way to get free food.
1) Type /who mage.
2) Check the list for a mage in your area.
3) Right Click on their name and press whisper, say : "Hey, if it's not any trouble, could i please have some food and water???"
4) Most of the time they will say yes, only 1 in every 5-10 says no... so it's a pretty high success rate. The +side is that you don't lose anything if they don't give you the food.
Hope you enjoyed this....and don't flame it just cause it's common sense...
BTW an alternative to it would be to just roll a mage....but that costs mana to conjure the food :P.