What ingredients can I add to no-knead bread to extend its life?
Ken Forkish's Flour, Water, Salt, Yeast has a brief note on storing baked bread (page 77).


  I got over my aversion to storing bread in plastic bags many years ago, after trying all the alternatives and realizing nothing else keeps the bread as well. The crust will soften, but the bread won't dry out. The straight dough breads will keep for two or three days. The breads made with pre-ferments will keep a day longer than that, and the levain [meaning sourdough] breads from this book will keep for five to six days, if you don't eat it all before then!


I propose sourdough starter as an additive that should almost double the life of your bread. Unlike the fatty enriching agents you suggest, using a sourdough starter should minimally impact the type of loaf you are baking. The process for making sourdough bread is quite similar to the "no-knead" method you are familiar with, and the result is similar, albeit with a more complex flavor. The downside, of course, is the work involved in maintaining a starter.

With respect to using a plastic bag, I usually split the difference: I store the bread uncovered for the first day to enjoy the crunch of the crust, and move it to plastic after to keep it moist. Do make sure the bread is completely cool before putting it in plastic.

I would also encourage you to embrace stale bread as a wonderful ingredient. When I bake, I count on a portion of the bread going stale, and use it for toast, croutons, french toast, stuffing, panzanella, or bread pudding.