Some really good ideas posted. I do want to reiterate a few.
Tupperware beats Gladware for watertight seal.
That being said, the round Gladware with the screw-on lids do seal up quite well.
Ziploc bags are watertight.
Dehydrated foods are lightweight and quite convenient. I bring some of the same stuff I use for bicycle camping.
I do use 1 gallon Ziploc bags to contain any liquid-ish items even if leaking is not expected, (I was struck by a car a few years ago and everything in my bag ended up covered in peach yogurt).