This movie contains examples of the following tropes:
Creator Backlash: During a discussion on his Facebook page, Disney animator/story artist Tom Sito revealed that Sally Field wasn't happy doing this film. At the time, her career had entered a brief slump following the critical and commercial disappointment of Not Without My Daughter, and she frequently grumbled about having to reduce herself to voicing an animal in a kid's movie. Of course, given the kind of character she's playing, this attitude fits perfectly.
Peter washing Chance with a hose after Chance eats the wedding cake and Chance afterwards playing with a balloon and popping it.
Kate taking the pets on a car ride, which explains Chance's excitement when Kate has to leave for the stock drive in a later scene.
The kids playing Nintendo and Bob being invited to a barbecue, only for the kids to remind him that the barbecue falls on the day he had promised to take them to visit their pets. Thus the catalyst for the pets' incredible journey.
Kate finding the note she had written Frank that he had not seen, and then calling the pound to know if the pets are found before she realizes they're heading for home. This scene reveals that the pets' human family lived in Fresno.
That could also be deduced by looking at Google Maps, as the ranch was mentioned as being near the town of Bishop.
Following the above scene Kate contacts a park ranger who mentions that the wilderness is a dangerous place for pets due to bears and mountain lions.
Sassy observes the man (whose name is revealed to be Quentin) who found her playing the saxophone at night for the forest animals, while wondering about Shadow and Chance.
The man at the river bringing his goat Aretha into his house while he leaves much to Sassy's displeasure and coming back to find Aretha tied up and the house a mess.
Before crossing the tracks, the pets search for food in the dumpster but found nothing edible, much to Chance's disappointment.
Chance running full throttle into a sapling and then keeping on running (specifically the part where Chance implies that Sassy is fat when rushing off for breakfast) was done completely by accident by the dog actor. They thought it was somewhat hilarious, so they kept it in, with Chance saying "Whoa! Gopher hole!" when it happens.