A supply teacher will often find that their role varies from school to school and often even from class to class meaning that sometimes they will be working off lesson plans that have already been given to them and other times they will be responsible for planning the lessons, teaching them and also marking the work afterwards.
Supple teacher are often paid more per day than permanent teachers but it may be that they one get work for a few days of the week so that money needs to last them longer. Also as a supply teacher you will not be paid for holidays unless you are on some sort of a contract which states you will.
With the variety of the job, many people say they enjoy supply teaching and find it more interesting than teaching the same class day in day out, although you can be offered a longer term supply teaching contract.
You may actually find that you miss being able to build up a relationship with the children and also with the other staff members and you will need to be able to quickly adapt to new surroundings to enable you to do the job to your best abilities.