I need more storage on my laptop. What's the best option for me?

I have an HP dv6500. I need more room for my files, music, movies, pictures, etc. The most important thing is that my files are safe - I can't lose any of it. What's my best option? RAID? External hard drive? I could make do with 500GB but could easily use 1 or 2 TB. I can follow directions and handle some manual setup but I'm not really a techie so let me know if more details are needed to find a solution. Thank you!