Next you will need a tow rope which is the rope required to attach you to the boat. If the company you rent your boat from is one that has a lot of water-skiers and wakeboarders using their service then this is something they will likely have attached to some of their boats. Alternatively you can purchase your own and take it to the site. Of course if you are regularly using the same boat then it might make sense to leave one there.
With these two items sorted there’s then no need for anything else in order to get started. If you’ve never tried it then, you just need to find a boat hire and then give it a go! There are more items though that can make the experience safer and more enjoyable however.
First of all, you should always have a lifevest. These will mean that you will float should you fall over (which is likely to begin with at least) and that will prevent you from drowning.