I figured I should know how this stuff actually works, so I tested out some durations tonight by recording Greengrocer slowly eating [Meat Pie] (meal) versus [Iron Rations] (hearty meal), then later reviewing the footage and comparing timestamps when the items were consumed. I also tested duration of [Flask of Water].
As far as level 1 Halfling Druids are concerned...
They will consume 1 [Meat Pie] every 2,028 seconds (33 minutes, 48 seconds)
They will consume 1 [Iron Ration] every 2,028 seconds (33 minutes, 48 seconds)
They will consume 1 [Flask of Water] every 2,028 seconds (33 minutes, 48 seconds)
Conclusion: Halfling Druids get very hungry and thirsty every 33 minutes, 48 seconds regardless of what they are eating. It is probably safe to extrapolate these figures (relatively) across all races and classes.
In other words, I'm a bit of a liar when I tell you your Mammoth Steaks are actually going to last longer than your Rations. I can only blame myself so much, though... Norrath needs labeling laws!! It says RIGHT ON THE PACKAGING that it is a "hearty" meal!!
What's a grocer to do? /sigh
Here is the raw footage (or "prof" as it has somehow been labeled here), in all its seven-and-a-half-hour-long glory:
http://www.twitch.tv/portasaurus/b/535418454