These kids may have cancer, but that doesn't mean they're not just typical kids. In this case, typical kids playing typical blow-heads-off-and-guts-out kind of first-person shooter video games. It may just seem like just another way to blow off some steam, but Augustus takes his game playing very seriously. When Hazel questions why he saved some hostages in the game instead of himself, he responds heatedly:
"All salvation is temporary […] I bought them a minute. Maybe that's the minute that buys them an hour, which is the hour that buys them a year. No one's gonna buy them forever, Hazel Grace, but my life bought them a minute. And that's not nothing." (4.83)
Um... are we still talking about video games here?
The whole life or death situation that is inherent in video games hits close to home for Augustus. Like the hostages in the game, he recognizes that he and his fellow cancer kids are working with a limited amount of time, and that any time bought for them is precious and valuable. Even though the drugs they're on might not save them forever, at least they're saving them for now. And he's right; that's not nothing at all. That's definitely something.