Packitgourmet has fueled all the dinners on my trips for the past few years. [On a side note, I have tried the lunch and a few breakfast items, but they don't fit my style as well as the dinners, which I cannot live without at this point.] The standard double-portion cook-in-bag bag plus the instruction sheet weighs about 18 grams. A quart freezer ziplock weighs about 7 grams.
To me, the supplied cook-in-bag packaging is worth the extra weight and bulk because I would not want to rehydrate my dinner in my pot, or in a quart ziplock. In fact, I doubt a double portion would even fit in a quart bag or my 0.8 L pot (yes, I have caloric needs). I could take a single cook-in-bag baggie and just reuse it each time, but the mess and smell are a nonstarter for me since I spend all my time in some of the most serious bear country on the planet. The pleated bottom, stand-up capable bag the dinner comes in is really handy for processing, and I burn my trash at every opportunity. I do, however, make a pinhole in the top of the bag and squeeze all the extra air out, and then reseal it with some good tape to reduce the volume. I also fold the bag down and put some electrical tape around to minimize the shape.
I admit it's not the most minimalist packaging imaginable, but the savings from repackaging do come with some tradeoffs. Also, a lot of my long trips are in a sea kayak where weight and volume are less of a consideration. If I did a backpacking trip much over a week, maybe I would reconsider. But given where I live, I sort of doubt it. ;^)
Confession: I am NOT an UL hiker. Just a 'light' hiker.