DH J.D. Martinez
The final player on this list isn't a pitcher. Cardinal fans have a particular picture of J.D. Martinez in their minds after his swing took out the team's best offensive player earlier this month. The only way for Martinez to make amends for his errors would be to bring his above-average offensive game to St. Louis.
The Cardinals have been desperate for a consistent veteran presence in the heart of the lineup since Contreras went down. With Nolan Arenado's power being sapped by the Monstars of MLB and Paul Goldschmidt being taken by Father Time, the middle of the lineup has lacked the bop that is needed to make an offense go.
The addition of J.D. Martinez would provide some pop to a lineup that's desperate for it. Martinez hit a home run Friday night against the San Francisco Giants, and his slash line sits at .294/.333/.435 with a 124 wRC+ on the season. He is striking out at a rate greater than 30%, so that's definitely a concern, but he has been ever-consistent at the plate.
Martinez is purely a designated hitter at this point in his career, so he likely won't play the field at any point for the Cardinals. He has hit left-handed pitchers exceptionally well, something the Cardinals used to do well but hasn't in recent years.
The Mets are reeling recently, and given their owner's recent cryptic comments, they'll likely be sellers once again this trade deadline.
Martinez signed a 1-year, $12 million deal this offseason, so the 36-year-old likely won't require much in exchange for his services. Hopefully, if the Cardinals are buyers, this move is paired with the addition of a starting pitcher. Simply adding an aging bat with decent power likely won't move the needle this year.