A bike rack lets you carry luggage on your bike much more easily. With a rear luggage rack on your bike you can attach things directly, or use panniers, a top bag or a basket.
If you are using your bike for touring, you may want to get a front rack as well as a rear rack so you can use front panniers as well to carry your touring equipment. A quick-release seatpost rack is easy to use on almost any kind of bike if you have nowhere to fit a conventional rack.
Finance available on all baskets above £280