I think you cannot say like "eat X amount a day and you are fine" if the aim is to make food weight less. It just depends on so many variables. Like:
-what is the intended total calorie amount per day?
-how much there is fat in the daily meals without adding anything?
-how well does your body adapt to using fat as energy ?
-how well does your body perform under fat heavy diet?
If I remember correctly, Poppis Suomela was eating 60% of calories from fat while going to North and South pole. I have seen even figures like 79% on some polar discussions. Eating those figures starts to sound like a work! They do not begin with those amounts right away, but increase gradually at home before the trip to avoid fat diarrhea. They could also start with somewhat lower amount and add more fat when the body starts to crave more calories. Those amounts of fat could give big downgrade in performance unless you still eat quite a lot of carbohydrates, so make only sense if your total calorie amount per day is high enough. Also, without enough carbohydrates, you could end up in ketosis like in Atkins-diet, which would beat the idea of making daily food weight smaller.
Regardless of the fat amount, I think the safe way is to eat the same meals before the trip at home already so that the body does not need to adapt to anything while walking.
If it's just a weekend trip, I don't bother changing anything. The difference in pack weight is not significant for me - unless I'm training for a longer trip.
For 7 days or longer trip, I take some extra fat on top of all the fat that is already in the foods. I have been eating 40-45% of the total calories from fat, but I think I could go higher.
Not all of that extra fat is olive oil, I take some clarified butter / regular butter for variety. I feel the taste of olive oil is good with pasta and rice etc but oatmeal and mashed potatoes taste better with butter. One good, tasty way of digesting olive oil is pesto sauce. Great with pasta but unfortunately not multipurpose. Also a little less calories than pure fat.