Walmart may sell soap, deodorant, and Tshirts, but are they open at 2 in the morning when you are forced out? Perhaps in your area, yes, but the last thing you'll want to do after a personal tragedy like a housefire is take a trip to Walmart. And, sure, your relative may have stuff you can borrow, but the normalcy of having your own stuff, especially after everything else you owned was destroyed, is crucial for a time like this.

Moreover, Walmart doesn't sell copies of your important documents and a harddrive of all your computer data.

This style of "bug-out" bag is incredibly common among the more realistic group of preppers, and it lends itself well to larger scale tragedies, as well. If a hurricane or tornado comes through, those stores may have been hit or may be out of stock as everyone else scrambles to buy shit.

"Preppers" aren't all people like you who focus on Hollywood level tragedies like civil unrest and global market collapse. And, even if they do, they recognize that these smaller scale tragedies are far more likely. To be honest, a bug out bag with survival equipment is typically a larp.