Most people are pretty appreciative of help. To me a thank you is enough. More than that, what ever it is, is really nice.
I keep a lot of trails and woods roads open in our woods. We like to ski and I do some logging. We have a 70 year old neighbor who uses the trails to ride her horse on. Last fall, out of the blue, she gave me a card with a picture of her on the horse in our woods. There was also a $100 gas card. It said thanks for keeping your trails trimmed so nice. Here is some gas money for your saw. Pretty neat.