Like all official tools and supplies, sculpture items are usually grossly priced and no better than things you can find for less. Here's a short list of things that I have found to work wonderfully for me.
PVC rolling pin
Gone are the days when I used the acrylic roller. I find them to be overpriced and never big enough to do any damage. Unfortunately, larger roller are made from wood (and impossible to clean) or are expensive. Grab yourself a scrap piece of 2" PVC pipe and cut it down to size with a miter saw, hand saw, or really any kind of saw. It's incredibly quick to make a few different lengths as well.
Additionally, if you are working on a large scale sculpture, it can be used as an interesting hammering tool as well, haha.
Thermoplastics are incredible. I use them for eyeballs, teeth, and feet tie-downs. There's an infinite number of uses for the stuff. You can keep reusing the stuff over and over again. Just keep in mind that the stuff absorbs the oil from the plasticine and will discolor over time. It holds up just the same though. Just don't set it on a plastic surface while hot or it will adhere to it.
Small Angular Brushes
You want to make sure to get the kind designed for oil-based paints as the clay is oil-based. The 1/4" brushes are a nice size to work with for smaller models, especially when it comes to smoothing out the eyelid area. I use them inside of the elbows and knee joints.
Cheap wide brushes
You can find them for few bucks at craft stores with a 40% off coupon. The softer the bristles the better. I use them to brush off clay burrs from hair that I have carved out. Chop them down to size (12" down to 5") as they are unwieldy and will keep you from getting at some angles.
Very rigid, clean cutting foam that comes in different sizes. I used less than half of the 1/2" 4x8' foam sheet to bulk up "The Big Pig" armature. It's incredibly light, can be hot glued together, cut with a Dremel. This leads me to my next choice:
I wrap the Foamular armature build up with this stuff. It keeps the clay from ever leaching into the foam (I don't know if it would break the foam down but I'm not going to find out) or being contaminated by pink crumbs from cutting it with the Dremel.
You can also wrap the odd sizes of clay with it. It works the same way as Saran wrap, but you don't have so much waste since they come in narrow sizes.