Most families or at least many were still in the tail end of the Great Depression. The approach was often kind of simple... If Dad was lucky enough to have a job, he brought his pay home. They paid the mortgage, the insurance on the house. They stuffed a dollar in a coffee can "for a rainy day". They bought basic groceries like sugar, and flour and bacon. Once in a while they bought new shoes for Jimmy, and Jimmy's old shoes got passed to Joey, and Joey's old shoes got handed down to Johnny.
If they didn't have a job, people lined up for work through the Civilian Conservation Corps. Forget preps. You got handed a shovel, a jacket, and three hots and a cot in exchange for 40 or 50 hours of manual labor. These CCC workers built roads in Yellowstone, dug drainage in Florida, etc. No preps. It was more a case of "this is how I get to eat today and tomorrow".
Preparations were pretty damned simple: A couple bucks a month stuffed in a coffee can. Mom tended the garden and canned everything except the grass. It was reuse, repurpose, or do without. There simply wasnt enough left over cash to be "prepping" as we know it. The root cellar was full of quart jars of green beans and beets, with a few bushel baskets of potatoes in the corner. There were chickens in the back yard.
If you look at world war 2 civilian life, its kind of evident that 'preps" were much more sophisticated. Ration books and coupons and product shortages were REAL. It was worse in the UK: Wolfpack U-boat tactics during the battle of the Atlantic came awfully close to starving Britain out of the war. Legions of British kids had vitamin deficient diets... A lack of vitamin C (no citrus) caused the Brits to search for alternatives... As a result, the Black Currant Cordial became a childhood treat and replacement source of Vitamin C. We event got this, I guess we will substitute that....
The government got caught off guard too. And it was more of the same "what will be good enough?". In a purely reactionary "Holy shit, this is desperate!" reaction we came up with items like the STEN submachine gun and the Liberty Ship.
I really dont think there was a lot of actual "prepping' in a "lets get ready for war" sense. Most of the USA was "we already fought a European war. No thanks. we are out of this one". Churchill wanted help, but we - by and large - opted out. It wasn't until the morning of December 7, 1941 that we woke up and thought "okay. Enough. Fuck it. Lets go kick ass".