I would not want to be seen in the vincinity of an ATM machine in the event of societal upheaval - if they're even working. Make sure your BOB has cash in smaller bills. $20, $20, $5, $1 denominations, some change for vending machines (food and water source) and maybe some 90% silver if you have a long distance to travel.
$100-$200 seems prudent. I'd do more if I were very long distances from home.
cash is good.
If SHTF, it will be more of "taking" or bartering if it lasts longer. gold and silver are good to have on hand as well as cheap alcohol ! I have several bottles of whiskey, cheap vodka, run and tequila as barganing tools (plus for medicinal purposes)