Might be something to file under the "you know you're old when..." thread, but when I was in my late teens/early 20s I'd keep an emergency $1 in the glove compartment for gas. This would have been late 60s/early 70s when that dollar bill would buy you 3-4 gallons.
There was a gas station near the college I went to where they never even raised an eyebrow when one of us would stop and ask for 28¢ (or whatever amount we dug out of the seat cushions) worth.
Surprising to see the number of $2 bills on that graph. Can't remember the last time I saw one of them, wasn't aware they even made them anymore.