Modesty
Rattleshakes do have a sense of modesty, and will almost always wear clothing. While it can be tricky at times to find clothing in their sizes, they are widespread enough that there are some options catering to them and other smaller species. In a pinch, more resourceful shakes have been known to steal and utilize doll clothing. Others frustrated with their lack of fashion options may choose the more ethical route of learning to sew themselves, which poses its own set of challenges given most sewing kits are scarcely designed with tiny hands in mind.
Core Temperature Regulation
While the liquid inside of a rattleshake has a temperature it naturally wants to remain at, and on some level will automatically maintain homeostasis, clothing can assist in this process. Those with warm cores will tend to wear warmer clothing to keep them that way, those with cooler cores cooler clothing to avoid overheating, etc.
It is for this reason that cloaks are particularly fashionable amongst the species; they come in both light and heavy and are easy to throw onto the torso.
Fashion Standards
The way that rattles dress themselves does not differ that much from how a normal skeleton might, with one key difference, pants. Given the lack of legs, such things are unfortunately out of the question. This doesn't mean that rattles don't get creative with other options. All manner of shirts, hoodies, cloaks, and jackets are worn, as well as accessories such as scarves, gloves, jewelry, etc. Some shakes may even wear skirts, as having legs provides no such obstacle in their usage. Those with horns or wings may adorn them as well.
Since so much of their clothing has to be hand crafted/commissioned, many take the opportunity to carefully curate an appearance that matches their core. For example, a lemonade core may intentionally incorporate lemon slice shaped buttons into a shirt, a shake with a floral tea core may have a blossoming pattern on a jacket, etc.
Ve-noms and vile vials tend to dress in a more intimidating or 'edgy' manner than other subspecies, with statements such as spikes being fairly commonplace.
Tail Decorations
As cracks are considered a sign of struggle and aging, some rattles will seek to cover them up. One popular way to do this is with stickers on the tail, though these will often come off with how often the tail moves, and are often reapplied. Ve-noms and vile vials are more likely to embrace these cracks and chips, some even displaying them with pride, as they are considered among some rattleshake circles a sign of survival and the overcoming of adversity. Some will even highlight their cracks by gilding them or painting them, to make them stand out.
Jewelry is sometimes worn on tails, with bands being worn near the tip where they don't get in the way of slithering. This can even serve as a way to highlight tail tips, either as a fashion statement, or in the case or sharp or stinger-like tips, a threat.