I've probably made this recipe 20 times at least since Sarah first printed it. I, too, use walnuts, because they're what I have. I also double the walnuts and craisins in the recipe. I even made them once with a cup of chocolate chips, and amazingly, I didn't like them as well.
I've tried cheerios, wheaties, corn flakes, and bran flakes, and I've settled on corn flakes as my favorite cereal for them. I sometimes make two batches at once and cut each batch into 16 rectangles, then bag each one in its own baggie. They do keep just fine for several months - the longest I've tested their shelf life. Mr. B and I almost always take one each for our day trips, year 'round, which is why I make them so often. And of course, they're great for midday eating on our backpack trips. They do tend to get really hard when the temperature is below about 25 degrees, so if we take them on snow trips, we try to remember to put them in our pockets for awhile before trying to break our teeth on them. Someone in the first thread had asked about whether they have a strong peanut butter taste, and they don't. All the tastes blend nicely together.