Say for the average home consumer, who doesn't think too much about security or worry about losing data, but knows they should have backups. What are systems that are very affordable and easily forgettable once in place?

I know that a drive failure on our main computer would be catastrophic in terms of losing important documents, though mainly 10+ years of digital family photo's. But I'm really too lazy to set up any kind of back up system where I have to do anything. I also don't worry a lot about security. Really it would be nice to have something automatic and worry/thought free. Any advice?