You wouldn't go to Cancun, Rome or New Zealand without packing items appropriate for the trip -- so why should you go to the Black Temple or Karazhan any less prepared? Levenah of the World of Warcraft Livejournal community asked players, "What do you carry for a raid?" She personally slings an impressive number of potions, a good amount of weapon oil and holy candles, and what appears to be one banana.
Most of the respondents seem to carry multiple stacks of every potion and food available, which makes me feel slack -- back when I was raiding, I came with about 10 healing pots, a stack of plus agi food, and then five to ten or so of my choice offensive and defensive elixirs. Oh, and 20 of each poison and Flash Powder, and usually a small amount of the Blinding Powder that no one ever asks me to use.
I know that tanking and healing classes tend to have to bring more items than DPS -- and this isn't even counting all the various sets a druid has to carry! What's on your packing list for a raid?