Ever find yourself about to go head-to-head with the first boss and realize that you've forgotten something crucial? It happens to all of us, and for that reason I've compiled a list of essential items to double check before your invite. In the same way that relying on memory when you go to the grocery store inevitably means that you will forget the milk, having a written list helps make sure that nothing goes forgotten. Consider printing up this list and keeping it by your computer for a quick reference...
Flasks and Potions
As a Mage you should have Flask of the Draconic Mind on at all times while raiding. Depending on how long the potions lasts (which can be based on a number of factors), try to keep at least one on hand for each hour of raiding you will do.
You should also have a good stock of Mythical Mana Potion and Mythical Healing Potion. I try to keep at least 10 of these on hand at all times.
You will be called upon to provide refreshments for the raid, so be sure to have enough Arcane Powder for a couple tables (because inevitably someone will miss the first one that you drop).
You should also check that you have at least one Rune of Portals for the end of the raid. Is this absolutely necessary? No, but your raid leader will thank you for it and it is nice to stay within their good graces and offer services without being asked.
Cook -- Purchase materials for the Seafood Magnifique Feast (at least 10).
Engineer -- Make sure you have the materials for Jeeves, so that nobody has to waste time running back to a city for repairs.
Alchemist -- Double check your mats for a Big Cauldron of Battle.
General Items to Double Check
Have you made a fresh set of Mana Gems?
Is your gear in good repair?
Do you have new gear that needs to be gemmed or enchanted?
Are you wearing your fishing pole or chef's hat? If so, for pity's sake, take them off! (Don't laugh, it happens!)
Are all of your add-ons current? Do you need to run any updates?
If you are a frost mage, be sure to always have your elemental out.
Mage Armor only! Anything else will cause you to run out of mana too quickly.
Have you watched a video of the fight or read up on it?
Did anything get left out? What else are you sure to always have when you run raids?