1 - Sleeve clamp
Sleeve pliers, also known as crimping pliers, are the essential tool for making steel leaders. There are models for single sleeves and models for double sleeves. Personally, I use the HPA model, which is of good quality, small and equipped with a cutting tip for small steel diameters, making it possible to have two pliers in one!
2 - Cutting pliers
Wire cutters are used to cut steel wire. If you're building your fixtures in advance, a conventional pair of wire cutters will do the job just fine. On the other hand, if you're taking it to the water's edge or on a trip, a smaller model is preferable. In any case, if you plan to use large diameters of steel, such as 80 or 150 pounds, the pliers must be of good quality.

3 - Sleeves
Crimp sleeves should be chosen to match the diameter of the wire rope used. The inner diameter of the sleeves must be slightly larger than the diameter of the wire rope. There are two types: single and double. Single sleeves are only suitable for small wire diameters, while double sleeves, which I prefer, are more versatile for both small and large diameters.

4 - Wire rope
5 - Swivels

6 - Accessories
Depending on what you want to hook on the end of your line, you'll need treble hooks or single hooks to make a stinger, for example, or staples and split rings.