Mathematics - school exercise books with 7mm squares for all ages, A4 or smaller. Amazon, Ebay, Rymans, WH Smith or local highstreet, HB or 2B dark pencils, rubber, Casio GCSE & A level approved calculator. Staedtler or similar mechanical pencils are good for older students, with 0.7mm graphite refills; HB or even 2B for a dark line.
English, Science, etc. - school exercise books, ruled and margin for all ages, A4 or smaller. Amazon, Ebay or highstreet.
Summary books - A5 "casebound", stitched, hardback or soft back notebooks. One per subject is best. Wilkos, WH Smith or internet. Some students prefer the "flash card" system using index files, notebooks are more robust and easy to carry; it really is a personal preference.
Written work - HB pencil and rubber for practise work, medium point black biro for finished work.
Extras - rulers, compass, geometry set, sharpeners, A4 or foolscap lever arch files, file dividers, 'Post-It' notes for page labels, graph paper.
Optional extras - crate or bookshelf to store books, highlighter pens, coloured biros and coloured pencils, flexible curve for graphs, Helix circle template.