Costco in California
https://twitter.com/lopp/status/1239676109731647491
I can give a first-hand report on two different Costos near me in the San Diego, California area.
Toilet paper and bottled water got hit hard over a week ago, but everything else was pretty normal. I have plenty of TP and water already, so that didn't bother me. No long lines, no problem buying food. My impression is it was just the actual preppers and opportunists that were doing mass purchases at that time.
Friday, after Trump finally declared a national emergency, was when everyone else reacted all at once. That was the day all the Costcos had lines around the building. Walmarts too (most of them have very large food sections) for that matter. I saw the lines, but I did not try to enter.
Saturday afternoon, things were back to normal. It was actually less busy than usual and nearly everything was restocked or in the process of being restocked -- there were lots of stock people working their butts off, but clearly Costco's supply chain was up to the task. From the chatter, I picked up that the freezer cases had been almost totally emptied the previous day. Still no TP or water, the pile of eggs was a quarter the usual size, and the quite large pile of SPAM cases were marked "one per person".
I also stopped at a Dollar Tree(everything is $1 each, before tax). They did have TP, if you were willing to pay a buck/roll....so it wasn't completely unobtainable. I was there to get several 2.5 liter bottles of Shasta root beer for a buck each.
Haven't been shopping since. I normally have enough of everything for months, other than perishables which can be done without, so you can call me prepared, but not a true prepper.