Every item in World of Warcraft has an internal Item ID and can be used from any macro with the following syntax:

/use item:ItemID
Macros of this type use the first item in the list you have in your inventory and ignore the rest.

Using this syntax it is possible to make one macro for all mage food and water when you first start dualboxing and not have to worry about changing it until you hit 70.

The following macros contain all ranks of mage food and water, in order from lowest to highest, in two macros.

FOOD
/use item:1113
/use item:1114
/use item:1487
/use item:5349
/use item:8075
/use item:8076
/use item:22019
/use item:22895
/use item:34062



WATER
/use item:2136
/use item:2288
/use item:3772
/use item:5350
/use item:8077
/use item:8078
/use item:8079
/use item:30703
/use item:22018
/use item:34062

You can also make similar macros for pots and other consumables:

BANDAGE
/use item:1251
/use item:2581
/use item:3530
/use item:3531
/use item:6450
/use item:6451
/use item:8544
/use item:8545
/use item:21990
/use item:21991

MANA POTS
/use item:2455
/use item:3385
/use item:3827
/use item:6149
/use item:13443
/use item:13444
/use item:28101
/use item:32948
/use item:22832


HEALTH POTS

/use item:118
/use item:858
/use item:1710
/use item:3928
/use item:4596
/use item:13446
/use item:22829


I have other consumable macros for cooked food and other things. These macros all use lower items first then move to higher items as inventory depletes. You could reverse the order to use higher items first.

There are mods that will tell you an item's ID in game. Or you can go to wowhead.com and just copy the ID out of the URL. The itemid URL parameter on wowhead uses the in game ID's so you can copy them from there.