Aren't milk in barrels limited to 25 or 10 units? And cheesemaking limited to stack of 5 each? I haven't milked and processed cheese in 2010 version yet, but that was how it was in 40d.
I would imagine the largest stack would be from butchering massive creatures that you could breed, like Roc ( which have 500 some units of meat each, according to wiki ) and roasting it, making at least [2000], however it's a megabeast so that's a bit difficult to make an industry out of them. The next most massive creature I know of is elephants, which would provide around a hundred stack of meat when well-bred ( however this won't work very well in versions with pastures, without adjusting the grazer value. )
http://df.magmawiki.com/index.php/DF2010:List_of_creatures_by_adult_size this could help, though.
And stack of 20 plants from potash? I thought the maximum was 12, and that's getting very lucky

Wouldn't have any idea of value, you could cheat and use dragon meat, which have 15x value, though only 110, 130 stacks of meat ( just checked in arena mode )