Carrying two weeks food is NOT unreasonable. I have done so many times. The trade-off is extra weight for the freedom not to have to walk out (perhaps round trip of 30-40 miles in some western mountain ranges) to resupply. Of course, an alternative is to get food packed in by horse outfitters, but you are talking $400 range of prices.

All my longer trips were done with an external frame pack- they offer very flexible capacity and carry heavy weights better. I still use my old Kelty pack, with an extender bar, in these situations.

You still need to minimize gear and watch the weight of the food, and re-pack it to eliminate bulk and packaging materials. Try to keep the food weight under 2 pounds per person per day- quite easy to do. I can get 2,500 calories per day with 1.3 pounds of dry/FD food. If you are a good fisherman, you can cut this back to about 1 pound per day. So, an average number would be about 1.5 pounds per day x 14 days= 21 pounds food. If you keep your base weight to about 20 pounds (light but not UL), that is a starting pack weight of 41 pounds. Not unreasonable at all.

Be aware that there is a "sweet point" of optimum pack weight beyond which it will slow you down so much that you do not gain much for going out more days in one food ration. Everyone is different. My "sweet point" is 40 pounds- Although the first few days are slow, I can still cover a lot of ground as the pack weight goes down. Yours may be different. If you are big, young and strong and can carry 65 pounds without slowing down too much, that is OK too.

Now, if your base weight is more like 30 pounds and very bulky, going out for 2 weeks becomes quite difficult.

The current trend is to go "fast and light". Long distance backpackers (on trails) now go 20-25 miles a day and cover so much distance that they seldom carry more than 4-5 days food. This is how PCT and AT hikers do it between going into towns.

Personally, that is not my style. I like off-trail and going a slower.

At any rate, I doubt you need a 90L pack. Maybe replace a few very bulky items (such as sleeping bag and tent) with more compact and light versions. Then ruthlessly delete the unneeded.