Almost anything can be used as a sculpting tool for clay which allows for a lot of opportunity and creativity.
I’ll go over some of the more basic and commonly used tools for miniature clay sculpting and then some lesser traditional tools that have been suggested to me from fellow keycap artisans and others that I’ve found to be useful.

Wax Carving & Dental Tools
These tools typically come in a fairly wide variety of tips and shapes which are usually pretty small in size and makes them pretty good for sculpting small things in clay. Most of them are solid steel and will usually have textures on the handles. The textures on the handles are also useful for adding textures to the clay.

These can be found at many places and all over online. Amazon.com has several options.

Silicone Tipped Sculpting Tools
These seem to be a favorite among many keycap sculptors that work with clay as they are really great for moving small amounts of clay around without being too aggressive such as with rigid tools such as metal or wood. They are great for smoothing out clay, removing finger prints and small dents and flaws as well as making smooth transitions between two sections of clay. These are available in some different shapes and sizes and also in softer to a bit more firm. Personally I prefer the firmer versions as I work with Monster Clay Hard and Medium.

These are also widely available on Amazon.com

Ball Stylus
Usually these tools come in a wide range of sizes and are typically double ended. They are great for indenting the clay with round shapes, creating eye sockets, meshing two sections of clay together, making dotted patterns and creating smooth grooves etc. Generally I personally stick to the smaller sizes for the miniature clay sculpts.

Also widely available on Amazon.com

The Monster Makers Stainless Steel Tool Kits
The Monster Makers is the company that makes Monster Clay which is a widely popular choice for many keycap artisan makers who work with clay. The company offers some different sculpting tool kits on their website which are somewhat unique. Namely two of their kits are very handy for miniature sculpting. The Precision Set (pictured below) and the Ultra Detail Set.

You can find these on the Monster Makers website.

Loop and Ribbon Carving Tools
These are very common among clay sculptors and can be very handing for carving away large or small amounts of clay. They are also great for carving away at round surfaces while maintaining the same round curves of the sculpt. One problem with these however is that they are fairly difficult to find in small enough sizes that will work well with keycap making.

These are widely available on Amazon.com, art supply stores and clay tool supply stores.

Ear Wax Removal Tools
Some of these are similar to the tools found in wax sculpting sets but are usually with shorter handles. They are good for creating different textures and lines and the spoon shaped tools can also be good for meshing two sections of clay together.

Found an Amazon.com

Improvised Tools
This is where you can start to get creative with which tools and objects you can find that you think will work good for sculpting small clay sculpts. In the photo below is an Exacto knife which will accept several different shapes and sizes of razor blades. These are very handy for both cutting and carving in clay. Next is a larger sewing needle, these are great for adding small details, textures, lines and can also be used for meshing two sections of clay together. The back end of the needle has some clay stuck to it acting as a handle to be able to better grip the needle. Next to that is a syringe with a fine point blunt tip needle. These can come in a variety of thicknesses from very thin to quite thick. The really thin ones are very handy for extra small details and getting into very tight, hard to reach areas where your other tools might not be able to. Continuing on are two different tweezers. Generally I will use these for carefully removing pet hairs that end up in the clay or removing sections added to the sculpt that I changed my mind on or need alterations before being attached to the main sculpt. They can also be handy for different texturing and small indents etc.

Improvised Tools Continued
Another fellow artisan keycap maker suggested the idea of making your own tools with some pens and custom tips. Find some pens you don’t mind ruining, open them up and remove the ink cartridges. Then fashion some different tips to your liking and bond them with the cone of the tip of the pens. You can use JB Weld, hot glue, super glue or similar to fasten them. Just make sure they’re fastened nice and tight and can handle a bit of force without breaking the bond.
The left most pen has a gum stimulator tip glued onto it. These are really handy for miniature clay sculpting. They are made of a somewhat rigid rubber and have a very fine tip on them. These are very cheap and can usually be found in packs of 3-5 pieces for less than $10 as Gum Stimulator Replacement Tips. Also found on Amazon.com.

More Improvised Tools
Continuing with a few more examples of items that can be great as sculpting tools. Pictured below on the left is a small piece of wood with a specific shape carved out on the one end. This technique can be used to make all sorts of different shapes and tips, both for carving, making grooves, lines and also making patterns. Next to it is a similar piece of wood with one end sharpened to a point and the other carved to a special shape. Next to that is an Allen wrench or hex key which I used to create a honeycomb pattern in clay. And lastly is a very small plastic screw driver with different tips on each end.

Extruder
This is a newly added tool to my arsenal which was suggested by another fellow keycap artisan and it’s really handy! This allows you to fill some clay inside and extrude the clay into different shapes and sizes. Very useful for creating uniform extrusions and sectioning clay into identical sizes. Some of these can be pretty weak and won’t be able to handle stiffer clays very well, make sure you find a good one. Below the photo is a link to the tool in the photo which works really well and can handle stiffer clays quite well.

This particular model can be found on Amazon.com.

Dental Alcohol Torch
Fire or heat in general is a great element to use for wax based clays as it will smooth out the clay quite a bit and also add a nice glossy finish to it. This dental torch is really handy as it can be filled with different alcohols that burn well and it features a small air powered torch that generates a concentrated flame as you carefully squeeze the bottle. Something to note about this however is that it is obviously not the safest tool, so it should be used with caution. The marbles inside the bottle help to weigh down the bottle to prevent it from tipping over as easily.

This can be found on Amazon.com.