During the week, apart from paper rounds, there are very few jobs which you can do. This is because you're only allowed to work a maximum of 2 hours per day and, apart from newsagents, there aren't many employers who need staff for such short periods.
On Saturdays you might be able to find a job in a shop, or on a market stall, but you're still limited to a maximum of 5 hours work.
Whenever you work, you must have a permit from your local education authority. This can be withdrawn if your school believes that your employment is interfering with your school work.
Most local education authorities have information on their websites about the rules for the employment of school pupils but East Sussex Council has produced a leaflet, designed to be read by young people, explaining the rules. It's available, in PDF format, here:
http://www.eastsussex.gov.uk/NR/rdonlyres/BECDBB47-5AFC- 4265-96E3-8AA4F3F88DFE/0/employmentyoungpersonsguide.pdf
Chris