Here's a few of the quick and lucky ones I found in an old portfolio I used to use. These have to be at least twenty five years old.
I do think drawing caricatures can be good practice. Ward Kimball once demonstrated to a group of us that he used to draw caricatures taken from photos of un-famous citizens in his local San Gabriel newspaper. One tip he pointed out was that photographs of small groups of people lent themselves better than "single" shots, because in the groups you'd notice right away a range of contrast and differences.