I'm glad to hear all the picking-up coins stories. My spouse ladles a generous measure of scorn on me for this and last weekend I picked up 3 separate pennies in his presence. But then later that evening when a co-worker was giving me a ride home I spotted a twenty dollar bill flowing swiftly downhill in the gutter! Being attuned to looking for money on the ground I was able to react quickly and grab it.
Today I was loading up my metro card and noticed a card lying on the ground. You see discarded cards a lot (discarded! ha!) and the MTA instituted a $1 new card fee ostensibly to cut down on the amount of trash this created in the stations. While it's easy to avoid, I do see a number of people in my neighborhood or tourists downtown having to cough up a buck and it seems unfair. So, both for my own needs and out of a charitable instinct, I'll keep a couple extra blanks on me. I used the machine to check the one I had just found (sometimes they're expired or un-fillable for some other reason) and discovered it had $2.45 on it! Only a nickel short of a full fare, which I assume is why someone left it?
So, anyway, those are instances of acquiring money, not saving it, but, uh... seemed like they would fit in.