There's probably more, but the one symbol I'm aware of is the parents turning into pigs.
One thing to understand about Spirited Away is that in Japanese media, the world of kami, spirits, etc, is often depicted as a traditional Japanese city, much like the look of the buildings Chihiro and her parents stumble upon in the beginning of the movie. (Other examples I can think of are Kamisama Kiss and The Morose Mononokean) Therefore, it's like they stumbled on the Japanese equivalent of the gingerbread house. It comes off as similar to Hansel and Gretel, if instead of being threatened to be cooked, they were turned into pigs for eating the house.
But furthermore, as I recall, there might have been some dialog about it being "an abandoned amusement park." This is a reference to the Japanese bubble economy of the 1980's. It was a time of explosive growth in the Japanese economy. People indulged in their wealth, and one of the things they built was a ton of amusement parks. Eventually, the bubble popped, and those amusement parks were abandoned left and right, sometimes still to be found in the countryside, rotting away. https://www.tofugu.com/japan/japanese-abandoned-amusemnet-parks/
This all ties in with Studio Ghibli's intent that the parents gorging on food and turning into pigs is a symbol for greed and consumerism. https://www.boredpanda.com/spirited-away-chihiro-parents-become-pigs-meaning-studio-ghibli-hayao-miyazaki/?utm_source=google&utm_medium=organic&utm_campaign=organic
Also possibly related, is the fact that Miyazaki commonly uses the image of the pig in his art. He often draws people, and even himself, as a pig. In another of his movies, Porco Rosso, the eponymous protagonist is in fact a pig for most of the movie. It is implied that the reason he is a pig is that he prefers it to being human. Thus you might also read the pig as a lowly animal that is still in some ways preferable to a human. That Miyazaki is also known to be a staunch environmentalist only supports this interpretation.
The theme of greed pops up in other places in the movie as well. For example, No Face offers Chihiro gold, which she rejects, as she rejected the food earlier, and for that she survives, where the frog, who took the gold, ended up getting eaten.
