Keeping a stack of $5 bills handy will last you much longer than the bigger notes.
Me I keep some small bils, but I have a bucket of change (lots of quaters). If I am able to make any last minute purchases say a two gallon container of gasoline if I pay for it with a handfull of change anyone watching isn’t going to consider me worth robbing other than maybe the gasoline itself, where as some one pulling out a wade of bills would be like throwing blood in the water.
Plus the change actually has some value in the metal they contain, plus quaters make great shotgun loads for zombies. :-)
I have all kinds. There is “emergency” cash for when the power goes out for a day and the computers are down at the gas station or store. “Emergency” cash for that something on craiglist or the gun show.
And yes - $1, $5 and $10 (and lots of change) for buying a fresh loaf of bread or a gallon of gas after the SHTF.