There’s no point in taking photos while you travel if you don’t have any place to store them. More and more it is possible to keep pictures in the cloud, but with a back up drive (or two) you never have to worry about a company going out of business and losing your images, plus you’ll be able to access them even when you are offline. We have had good luck with Western Digital’s MyPassport.
A while ago, we wrote a blog post in which we claimed that a new MyPassport we purchased was a dud. We later discovered that it was our cheap USB hub that had killed it. Sorry WD. With backup drives, it’s tempting to go for the highest capacity ones because it means you have more storage in the same amount of luggage, but you don’t want to put all your eggs in one basket. If something happens to one drive, it’s good to know that other photos remain on another. Anything more than 2TB is excessive.