Trips gets to the University of Memphis in time to intercept the package, but realizes he is in love with Ivy, not Kimberly (and then it is confirmed Kimberly was cheating on him). Trips finds Ivy and the two share a passionate embrace.
Wyatt Trips (Paul Rudd) is in a long-distance relationship with his girlfriend Kimberly Jasney (Christine Taylor). He attends a university in Minnesota while she is enrolled at the University of Memphis. One night, Trips calls his girlfriend and Kimberly's roommate intimates that she spent the night with a guy named the "Ricker." Trips gets drunk and goes to a strip club with his friends where he befriends a fellow student/stripper named Ivy Miller (Reese Witherspoon). She takes pity on Trips and helps him write a mean break-up letter and poses for nude pictures to include in the envelope (to make it seem like Trips actually cheated on her). The pair then drop off the letter with an express overnight delivery service. The package is slated to arrive on Valentine's Day.
The next morning Kimberly calls Trips and mentions that the Ripper is a friend's pet dog that she is babysitting. Trips realizes his mistake and runs to Ivy for help in preventing the delivery. They go to the delivery service but the woman working there (a cameo by Sarah Silverman) had been insulted by Trips earlier in the film and refuses to cancel the delivery. They try to reason with the delivery driver (Larry Drake) to return the package, but being ultra-committed to his job, the driver refuses to give it to them.
Trips and Ivy eventually end up pursuing the delivery driver across the country. They bond and Ivy soon falls for Trips. Many hijinks also ensue, including Trips being held hostage by a serial killer, Trips' clothes destroyed in a highway chase scene, being arrested for a dash and dine, and Ivy's car falling off a cliff. The pair ultimately catch up to the delivery driver and end up accidentally blow up his truck. The driver somehow manages to get the largely-destroyed truck running again and vows to deliver the only surviving package, i.e., the one Trips sent to Kimberly.
Trips and Ivy steal a car from a drunk driver (rationalizing it is a net good deed) and make it to the University of Memphis. Trips runs off to stop the delivery (accidentally tackling and scaring off a delivery man who was delivering the flowers he had mailed to Kimberly) while Ivy hangs back, forlorn that she has lost her crush. Trips manages to stop the delivery just as Kimberly is signing for the package. The couple make out, which causes Trips to realize that he is no longer in love with Kimberly. He dumps her (on Valentine's Day) but then learns that the Ripper was actually a guy Kimberly was cheating on him (a net-win?). Trips leaves to find Ivy (and on the way, tells the delivery driver to deliver the package after all, thus making the driver's day). He finally finds Ivy and the two finally kiss.
Thanks Evan B!