When you have a few files or a dataset or two, it's not that big of a deal. When you've got years of materials or 200 PDFs of articles you need to read for a major project, then managing your data is a very big deal. There are a lot of ways to manage your data. The sites below offer a couple of options.
The above link to Endnote will take you to the Ablah Library Endnote guide. WSU pays for a license for Endnote. Endnote has a bit of a learning curve and is somewhat similar to Mendeley. Endnote will allow you to hook up to Word for doing citations, search multiple databases, take notes, tag, etc.
L - Lots
O - Of
C - Copies
K - Keep
S - Stuff
S - Safe
LOCKSS is a core principal in making sure your data doesn't disappear. The rule of thumb is that you want to back up your data often and in more than one place. Geographic diversity is best. While there has been an iCloud breakin, unless your data is sensitive, putting data into a cloud service still isn't a bad way to go.