This is an interesting thing I'm noticing as I'm reading but it kinda seems to me like a lot of the Tolkien characters all seem to have elemental symbolism that seems to follow their characterization.
Like Gandalf and Bilbo both seem to have a lot of fire symbolism that follows them around. Gandalf uses light and fire as kind of his two go to weapons and he's the keeper of the ring of Narya which is the fire one. And of course Gandalf the White is forged out of flame. And then Bilbo's introduced in the middle of smoking, and he spends a lot of time hanging around campfires and hearths, like the campfire storyteller he is. He seems to like hanging out in the Hall of Fire at Rivendell, and his conflict with Smaug obviously also involves a lot of fire. He's also arguably the character who is closest to Gandalf.
Frodo on the other hand is like all water imagery. One of the first things we learn about Frodo is his parents were weirdos who hung out in boats and then drowned, and he's introduced filling drinks at Bilbo's party. He makes his stand against the Nazgul at the river. He himself nearly drowns like three times in the story, and spends a lot of time in boats, being haunted by dark waters, and the sound of the ocean (and of course ends the story going over the sea). Like the water symbolism with Frodo is nonstop and he shares that in common with Gollum, who specifically is characterized by pools, rivers, and lakes, as well as fish, worms, mud and roots and caves—very wet and slimy compared to Frodo's more mariner/wayfinder imagery. But they're still kind of two sides of the same coin.
Pippin and Merry get a lot of plant and tree symbolism. Besides hanging out with ents and drinking tree wine and that time they both got eaten by a tree, it's clear Merry grew up wandering forests and knows a lot about wild plants (and writes a book on it later) and Pippin gets a ton of association with Gondor, y'know, that place that is represented by a big ol' tree. Their tobacco leaves too actually kinda play a pivotal role, and are again, very plant focused.
You'd think Sam would also be more earth oriented, being he's a gardener, but not really? Unlike Merry who's out here spitting plant facts 24/7 and working on his plant book, Sam's interest in plants seems like to only be around when he's on the clock. His symbolism is all very celestial. He's the guy who ends up using the Star of Earendil. He sees Earendil while he and Frodo are walking through Mordor. He evokes Elbereth, the Star Goddess like multiple times. He names his daughter after the star-sun shaped flower Elanor which literally means "Sun and Stars." And if you think about it, Gardener is actually kind of a perfect role for a star-guy when you remember how dependent plants are on the sun. He also seems to share some kind of connection with Galadriel who is also caked in a lot of star imagery. It also tracks he'd be paired with Frodo thematically as he serves as a guiding light to a mariner, in contrast to how Gollum represents the depths.
IDK what all that means, I just think it's neat!