taking a wild guess..or a good guess...

[twinkleblur]

how many flasks and buff potions would you say you would use throughout 1 expansion?

my total guess?

980 flasks

5000 buff flasks and if i were to add other stuff like mana pots health pots and stuff for fun? about 1k...your turn.

[Imnick]

~4 hours per raid, ~3 raids per week, ~12 flasks per week

Cataclysm released December 2010, MoP released October 2012 (actually September but I'm rounding it up because I like round numbers)
So that's ~22 months of expansion, ~88 weeks

Subtract two months worth of various missed raids over the expansion cycle, 80 weeks

80 * 12 = 960 flasks

So something like that? Pretty close to what you guessed

[Belize]

Not a lot, I always forget I have them :S

Guild doesn't mind though

[Winkleslob]

No idea, who cares?

But, to not be a complete douchebag and leave only that as a response i'm guessing i use about 1000 flasks, but 3000 buff food.

[FuxieDK]

In TBC, very few, since the marks from Tier 5 and Tier 6 raids were so abundant, that everyone had their needs covered in full..
In WotLK ~450 based on above calculaion, but half, since I'm alchemist.
In Cata, zero as there was cauldrons, which my guild provided..
In MoP, zero as I only raid LFR, so none is needed..

[K i s u]

To be honest i'm not quite sure, when i'm on an alchemist alt probably 90% of the time when i'm not I otherwise usually completely forget so I'll go with a low number 100-200 with it decreasing since LRF was introduced. I do however use my food buffs nearly constantly.

[-Superman-]

Pro Tip - You can go to the achievements tab in your armory, choose statistics, and view how many you have taken total and which one you use the most.