As Stanley digs holes, he loses track of the days. He thinks he's probably lost five pounds and reasons that in a year and a half, he'll either be dead or in excellent condition. His hands grow calluses and the shovel isn't as painful to hold. One morning, as Stanley digs, he notices something shiny in his dirt. He deliberates whether or not he should investigate but finally gives in to his curiosity. He discovers a thin, finger-length gold tube that's open at one end. On the closed end, he finds the initials KB inscribed in a heart.
When Stanley appears to give equal weight to the possibility of being either dead or very fit by the end of his sentence, it shows that he does still have his positive outlook on life, though it is being tainted by the toxic structure of Camp Green Lake. The discovery of the tube shows the natural world bestowing a gift upon Stanley, as nature has been hiding the tube for years.
Stanley tries to figure out how to get out of giving it to X-Ray. X-Ray's hole is almost finished, unlike Stanley's, and by the time the Warden deems the find interesting, X-Ray might already be done. Stanley wonders if he could take the tube directly to the Warden, who might then make up a story to protect him from X-Ray. As Stanley is trying to figure out what the object even is, Zigzag notices Stanley and asks what he has. Stanley takes the tube directly to X-Ray.
The fact that Stanley spends so much mental energy figuring out how to get out of keeping his promise to X-Ray suggests that he's taking to heart that justice is something that can be molded to meet one's own needs. It also shows that he has a long way to go to learn the lesson that Elya Yelnats didn't learn when he broke his promise to Madame Zeroni.
All of Group D crowds around X-Ray to inspect the tube. Squid thinks it looks like a shotgun shell, but Magnet insists it's too long. Stanley suggests that X-Ray wait to show Mr. Pendanski until the next day so he can have a whole day off, not just an hour. X-Ray thanks Stanley for his excellent idea and when the water truck comes, he tells Stanley to get behind Magnet in line.
When Stanley is rewarded with moving up one spot in line, it impresses upon him the importance of carrying through with his promises. However, it's also worth noting that the line order is a show of power, not anything that's actually based on merit, which illustrates the way that the camp co-opts things and makes them cruel.