Not to be a debbie downer, but I'm thinking we're already into the long slow descent into third world conditions ... the fizzle, not the bang. Things like intermittent power, intermittent clean running water, scarce food, scarcer comfort. Think the best preparation is to be as healthy as you can, require less to live and thrive, knowledge over things, quality over quantity, etc. Its 90% psychological - if you can't imagine living without X, then when X is gone so is your reason to survive. Probably the best thing to do is invest in your kids and grandkids so that they have the right mindset for it, along with faith and hope, and a few skills.
I've got the normal stuff covered, surviving in the modern world stuff, to bridge to the still expected return of normalcy that we all imagine the government will provide. But I think we're closer today to that "unexpected" day when no one will show up to turn the power, gas, water back on; the trucks won't restock the grocery store, and we'll be on our own. I hope to be retired and with family on that day. Until then, food staples, means to make clean water, cook food without electricity, and stay warm are on the top. Then protection.