Dennis Quaid's twins are extras in the diner scene. His daughter is the one who points towards Quaid's character during his health incident.
Dennis Quaid's character was a quarterback in high school. Dennis Quaid [not his character] also played a quarterback in Any Given Sunday (1999). If you notice the picture Bart has of his dad, it's a picture of Quaid in his #19 black jersey from Any Given Sunday.
In the movie, Trace Adkins's character tells Bart "Bring the Rain" boys when they got to Nashville for the GMA's. This would be the title of a hit song for the band in 2001.
During the opening scene set in 1985, young Bart is riding his bike through town. He passes a movie theater showing the titles Jaws 3-D (1983) and The Goonies (1985) on the marquee. Dennis Quaid, who plays Bart's father, Arthur, played the lead role of Mike Brody in Jaws 3-D in 1983.
Before Bart (J. Michael Finley) begins writing the title song, I Can Only Imagine, there is a guitar case in the background that says "I Can Only Imagine" on it.