I think it Goes With Out Saying that different people (on different hikes) are going to be eating different weights and volumes. But it's also handy to have a rule of thumb when you're planning your packing…how much will my food likely weigh? How much space will it likely take? I love having a formula, even if I later disregard it or find it is inaccurate.
The volume of food per day, in liters, that I've seen mentioned here at BPL, culling from a variety of different threads (yes, I actually take notes on forum posts!!) is: 1 liter — 1.2 liters — 1.5 liters — 1.6 liters — 1.8 liters. Obviously this also varies by how much you compress your food; if all your food is powdered and dry (poor you), likely on the low end.
And, if interested, I've also recorded reported weight per day of food, in ounces. From what I've read here at BPL:
19 — 20 — 21 — 22 — 24.
The above numbers have not let me down yet. I weigh my meals, calculate days out, and am pretty darned happy with how little I have left over at 22 ounces per day. Which is very close to the same number Clelland came up with, observing 10 people over 13 days of hiking.
So far, a medium size nylon freezer bag will nicely hold 5 days (7.5 lbs) of food — no catastrophes yet. I do carry tape in case I get a rip. I twist the end tightly, make a bight of it, and then wire-tie the bight in place with a Nite Ize Gear Tie. The loop I made of the sack's end gets clipped in a carabiner, and up it goes. I suppose it goes without saying that a nylon freezer bag presents almost no barrier against rodents. This, I have verified!