The Odd Couple II

It has been 17 years since Oscar Madison and Felix Ungar have seen one another. Oscar is still hosting a regular poker game and is still an untidy slob, now living in Sarasota, Florida, but still a sportswriter. One day, he is called by his son Brucey with an invitation to California for his wedding the following Sunday. A second shock for Oscarâthe woman his son is marrying is Felix's daughter, Hannah.
On the flight from New York to Los Angeles, it becomes clear that Felix has not changed his waysâhe is still a fussy, allergy-suffering neat freak nuisance. Oscar and Felix are reunited at the airport and very happy to be together again after 17 years of separationâat least for a couple of minutes. They intend to share a rental car to San Malina for the wedding. But the trip begins with Oscar forgetting Felix's suitcase at the Budget car rental, including wedding gifts and wardrobe inside. Oscar also loses the directions to San Malina when his cigar ashes burn them.
He and Felix become hopelessly lost, unable to even remember the name of the town where they are headed, so many California city names sounding alike. They end up in a rural area, where the car rolls off a cliff and catches fire. If that were not enough, they get arrested several times by the local police, first for catching a ride in a truck carrying illegal Mexican immigrants. At a bar in town, they meet two extroverted women, Thelma and Holly, and buy them drinks. Accepting an offer of a ride from a stranger even older than themselves, Felix and Oscar end up inside a $150,000 vintage Rolls Royce Silver Wraith with a dead body and get arrested a second time.
Irritated, exhausted and convinced that they'll never get to the wedding, they get arrested yet again for consorting with armed Rednecks who believe Oscar and Felix were flirting with their wild women, Thelma and Holly. The boys are freed and driven directly to the local airport by the police, who are only too pleased to be rid of them. A woman boarding the airplane is also en route to the wedding and recognizes them. She is Felice Adams, Oscar's ex-sister-in-law, the sister of his ex-wife, Blanche. Felix's eyes light up when he learns that her husband died of a heart attack. He calls her "Lise," which causes Oscar to ask Felix if she calls him "Lix."
They finally arrive at the right place, only to find that Brucey is having second thoughts about the wedding due to his parents' bad history with marriage. Felix and Oscar argue with their ex-spouses, after which Oscar persuades his son to go through with it. Felix's suitcase is returned and the wedding goes off without a hitch.
The next morning, Felix and Felice leave on one flight and part ways with Oscar, who returns to Florida. Oscar is telling his poker friends about the wedding when the doorbell rings. It is Felix, who says things with Felice didn't work out. Felix wonders if he could move in with Oscar until he finds his own place. Oscar says no, but eventually relents, insisting their days of being roommates will be over if Oscar catches Felix matching any of his socks. Before long Felix is cleaning up the apartment and Oscar is overcome with a sense of having been through all this before.

Question: What did Oscar forget at the Budget car rental?
Answer: Felix's suitcase.