Royal Mail are great for casual work. The hours offered vary, and the pay rate is good. You can put in as many or as few hours as you like. The workplace has a friendly culture, and everyone is keen to help one another, and the job of sorting mail can be quite varied and active. There are frequent enough breaks, and overtime is paid for well. Management can sometimes forget to notify you if your shift has been cancelled for a day, but if you don't find out until you get there they will often still find work for you to do so you haven't wasted a trip.
Flexible working times, enjoyable work, friendly atmosphere, good pay rate
Shifts are on a first-come, first-served basis, breaks can be short (and are deducted from pay)