"Luck is when preparedness meets opportunity"
I know my guildies are sick of me talking about this when we raid. As a mother and raider its my job to remind folks when they raid to come prepared. Nothing more frustrating than having folks arrive without flasks, food, bullets, reagents, pots etc. Regular raiding is expensive but if you plan to raid then you have to come up with a way to make gold to pay for supplies.
Of course people forget from time to time and I don't mind helping them out but its the people that show up regularly unprepared that put me over the edge. It is particularly important to come prepared if you are undergeared or your damage is very low. Flasks and buffed food make an incredible difference in damage/healing/tanking. If only 2 people are left on a boss and his health is low, it could make the difference in taking him down.
ie. My hunter hubby was in MT on the final boss, Kael'thas. He had taken a plus 30 stam food before the fight and was the last man standing with 290 health to take the final shots. Without that buffed food it would have been another wipe.
Don't let people carry you through a raid. Do your best to be at the top of your game. White damage is embarrassing and your toon should not just be on auto pilot when others are workin their buns off. I don't expect everyone to be top damage; (I'm certainly not) however, I do expect people to put in the effort.
Make me proud and don't be a burden to others when you raid. Come prepared.