We use the following labels for things like lunch boxes/shoes, water bottles, DD has been at school nearly a year and we still haven't had to re-label anything, they even survive the dishwasher and are fairly cheap.
cgi.ebay.co.uk/50-Waterproof-PVC-SHOE-Name-Labels-School-Name-Tags-/310080541840?cmd=ViewItem&pt=Boy sClothing&hash=item48323d9490#ht3498wt1137
For shoes we use the link below, doubly useful if your DC can't tell which foot each shoe needs to go on, as the label is in the shape of left/right foot. Again these have lasted the life of the shoe.
cgi.ebay.co.uk/10-PAIRS-PRINTED-SHOE-NAME-LABELS-TAPES-TAGS-/260609439140?cmd=ViewItem&pt=UK_Clothes ShoesAccessoriesBoysShoesBoysShoesJN&hash=item3cad8875a4#ht3271wt_1137
For clothes we use Cash's sew in labels (I only sew each end of the label) and I keep a permenant /dvd marker to hand for last minute labelling or writing on the bottom of PE socks.
If your school has a theft problem , then it's worth writing your childs's name in inch high lettters on the inside of the sweatshirt/ jumper ribbing round the waist (test first to make sure the ink doesn't run through).