Another useful tip if you’re a Mac user: Get yourself a cheap 8 GB flash drive and make a bootable OS X installer using Diskmaker X and stow it in your backpack or laptop bag. You never know when it will come in handy, it takes up very little space, and you’ll never regret having it. If you’re on the road and you need to perform a fresh install on a new drive it’s a lifesaver. The flash drive seen here is the smallest I’ve ever owned … it’s barely bigger than a thumbnail and it’s been my go-to OS X install drive since Lion (10.7).