Helmet may be smart, but making sure you can still skate years ahead is not the worst idea in the world.
Knee pads, elbow pads, crash shorts, wrist guards. The main suggestion as far as a pad goes is definitely knee pads. In both skateboarding and longboarding, you will find when you fall you can mainly fall to your knees and protect everything else. If you feel like you fall a certain way more than others, you can always look into getting more protected with elbow pads. Wrist guards are mainly used in skateboarding because in longboarding Slide Gloves do a great job at protecting your hands. Crash Shorts help protect that booty... and your hips, and pretty much anywhere where all of your weights gonna slam on.