When Clara's wagon fell into the ravine, we see clearly that all of her luggage was lost. There was no luggage on her horses or on Doc's horse after he saved her. How does she later have large suitcases and a telescope?
This is answered in the movie, and serves to further Doc and Clara's flirtation. She clearly mentions that her telescope was broken during the accident, not beforehand :
CLARA: When my bags were thrown from the wagon, my telescope was damaged. Since you mentioned an interest in science I thought you might be able to repair it for me. I would pay you, of course.
Despite what we see, we have to assume that she somehow retrieved some or all of her luggage. There's no reason to think otherwise. She could possibly have bought a telescope and broke it just to seduce Doc. Given that this is the old west, she can't just go down to Wal-Mart and pickup a telescope, so it's likely she's telling the truth.
Maybe a party hiked down into the canyon and retrieved some or all of her baggage. It's left to our imagination.
This was addressed in the film's official novelisation in which we learn that most of her luggage fell off the wagon before the wagon went over the cliff.
But he was gaining on the careening buck-board! The horses pulling the wagon were galloping wildly, jerking the wagon back and forth in a zigzag line, while Doc’s trusty horse, Archimedes, was heading straight and true to Intercept the buggy before it reached the precipice. In mere seconds, Doc and his steed had drawn parallel to the rear of the buckboard - close enough to see the trunk and travelling bags leap with every rut and protrusion the wagon wheels encountered.
The buckboard hit a large rock, turning over and dumping its contents on the ground before it flipped over a second time, falling over the edge into the ravine.
We can see some of this luggage being ejected in the film.
I can think of the following possibilities how this might have occurred though I have not found any specific canon support for them. But just from personal moving experience I think these are plausible either alone or in combination.
Clara shipped items ahead: Clara was moving to Hill Valley. Even though in the 1800s people often had a lot of items to bring with them when moving. I suspect what she had in the wagon with her would only be the most valuable items she wanted to keep a closer eye on.
The school board and parents provided items: Townships in the 1800s often sponsored teachers and provided room and board in addition to salary. It is not improbable that the town might have realized a young teacher coming to town might not be able to ship all her items so agreed to provide some basic items either in lieu of salary or perhaps as an advance against salary. When I moved for one of my jobs the company provided a temprary moving allowance benefit at a company furnished apartment until we could get settled. Perhaps that is what we see for Clara.
The town provided some items to temporarily replace what she lost. I.e. The town might have simply pitched in to provide some items out of charity. Carrying them over in luggage bags simply was easier.