Other than the obvious things like dies and shellholders, you don't
need any additional items, but there are some things that are nice to have.
case mouth chamfering and deburring tool - touches up the case mouths, also makes seating bullets a little easier.
primer hole deburring tool - removes the burr on the primer hole inside the case - required on some new cases.
primer pocket cleaning tool - these can be motorized or manual, they simply rotate inside the primer pocket to clean it and allow the primer to seat better.
There is more stuff you'll pick up as time goes on (trimming tools, case length guages, OAL guages, etc., etc., etc.).
Pay heed to Cheapo's admonition about using case lube and don't forget it when resizing. But when you do forget (we all have at one time or another
), a stuck-case-removal tool comes in mighty handy. They're cheap and will pay for itself the first time you need it.
If you don't have any loading manuals, buy two or more and read the front sections of them. They have very good advice on most all aspects of reloading.
Lastly, reloading for semi-auto and lever rifles takes more care than bolt actions. If your ammo for the SKS is not as functional as factory loads, you may need to get a "small base" die. They are better at full length resizing than standard dies. Also, for semi-autos, you will need to pay more attention to the crimp. You may need to get a crimping die like the Lee Factory Crimp die.