I flew the J32 Jetstream for American Eagle in the early 1990s. IIRC, the F/O pay was $15.50/hr so about $15,000 per year.
The J32 had only a curtain separating the cockpit from the cabin and our two flight bags, almost always the big leather flight cases back then, sat in the middle giving the passengers a full view of the ends of our bags. One of our F/Os taped a copy of his year-end W2 form to the end of his flight bag for all the passengers to see. I don't remember anything every coming from it.
The only time I've been tipped was when flying Grand Canyon tours and that was still pretty rare.
At the Major airline, a passenger will occasionally bring something from the crew but it's never been money. Closest was a $5 Starbucks card for each crewmember. Other times it's a small bag of chocolates given to the F/As.