It was a collection of short stories. I can't remember how many.
The first one I remember quite clearly. It was about a family who goes to the seashore for summer vacation and the brother and sister fight a lot. The family goes to the beach and the boy wanders off and passes out because of heat exhaustion. When he wakes up a black car drives up to where he's laying on the sand. The driver, an old man dressed in black like an undertaker gets out and opens the back door where a woman is sitting. He motions to the boy to get in and tells him "You're next". The boy runs away to find his family has left the beach so he goes to the beach house they are staying in for the summer. He tells them about his experience and they convince him that he just imagined it. Later that night they go to this amusement park nearby. The brother and sister are excited to ride the old fashioned wooden roller coaster, although the parents express concern. When the two siblings reach the head of the line, the attendant turns out to be the old man the boy met on the beach earlier. He holds the door to the roller coaster car for them and says "You're next" like he did before. Also sitting in the car behind them is the girl from the car. The boy grabs his sister and runs away as he hears behind him as the roller coaster collapses.
Ring a bell for anyone? I remember getting this collection as a present from my parents for my birthday or Christmas when I was in junior high-late 80s to early 90s.