A good helmet protects your most important vital organ. Remember that in some states helmets are required by law. In Oregon, for example, skaters 15 and under can be fined for not wearing a helmet. Knee and elbow pads will also save you from bumps and bruises. Knee pads are particularly valuable when learning to skate tall vertical walls because they allow you to slide down the wall on your knees instead of having to run out of every bailed attempt. Wrist and ankle injuries are common in skateboarding, so braces are another great investment.
Without good grip tape, skaters have a tough time staying on top of their board. The main complaints about poor grip tape tend to be that it was never very grippy or lost its grip really quickly. Once again, we recommend trusting in name brands with years of experience supporting skateboarders. Unfortunately, if you are buying a pre-made complete skateboard, you probably won't have access to the brand name of the grip.