This is a habit I've had since I was a kid - I pick up loose change wherever I find it. Usually whenever I buy something from the vending machines downstairs, I check all the machines as I'm walking out to see if there's any change there. Usually it goes into my purse, and then into my piggy bank at home.
I think I started this when I was a kid mostly because I loved coins, especially silver coins. Pennies just didn't seem worth the while. I used to sell stuff I found on the street to the other kids on the street and buy Bubble Tape with it. When you are a kid with no allowance, it takes a lot of crap on the street to buy you a 75 cent roll of Bubble Tape. However, I recall eating a lot of Bubble Tape as a kid so I must have done OK.
Some of my frugal habits have started rubbing off on my coworkers. One of the student workers has started bringing in a can of Chunky soup every day - she got the idea one day when she was hungry and didn't have any money on her, so I pulled open my desk drawer and offered her a can from my selection. (She still usually comes in and asks for a bowl and spoon though - I am the queen of disposables.) I also only buy a bottle of Powerade maybe once a week or less. The rest of the time, I use the same bottle over and over with Crystal Light in it instead of Powerade. Better for me (a bottle of regular Powerade is about 160 calories, whereas a bottle of Crystal Light is 10) and better for my wallet (Powerade is $1 a bottle; Crystal Light is about $4 for 14 packets, and the water is free.)
All that frugality pays off though - yesterday was Boyfriend's and my two year anniversary and we went to The Melting Pot, a swanky fondue restaurant. Total bill was about $120 but I paid for it straight out of checking. (And then on the ride home we had a conversation about how we could make it cheaper if we ordered separate entrees instead of the two person one, didn't get lobster tail or filet mignon, and didn't get salads.)