A large basket or wickerwork packing-case with a cover used to pack or transport food and/or drink (what in the U.S. would be called a picnic basket). By extension, the term is also used to refer to a present of a consignment of food in any type of case or box (NSOED).
happy Christmas (British edition only)
Equivalent to "merry Christmas", of course. Worthy of mention because "happy Christmas", while perfectly understandable, is not the form commonly used in the U.S.
Come on...look round...I'm sitting here all alone... come and have a go...
"come and have a go if you think you're hard enough" (DH21)
Using this word to refer to human provisions is a little like speaking of "feeding and watering" people or referring to food for humans as a "nosebag", because like those expressions 'haversack' originally was used to refer to feeding horses rather than people. The word was originally borrowed from French (which spells it differently), which had borrowed it in turn from German Habersack, and meant a bag used by cavalry to carry oats for their horses. In English, haver is a dialect word for 'oats', used in Scotland and northern England. (NSOED).
a haversack large enough to carry several small children (OP20)
Many secondary (12-18) schools have a Head Boy and Head Girl. These students are sometimes chosen, by the teachers, for their excellence, but they could also be elected by their peers. The Head Boy and Girl represent the school externally and head up the prefects. See also Prefect.
In Britain, "holiday" can refer to any day or time off (as in leave from work) rather than just a vacation or official holiday. National holidays are usually called Bank Holidays, because the banks are closed.
'weren't going home for Christmas because they wanted to spend it alone. You know, first holiday after they were married.' (DH20)
Someone on holiday, i.e., on vacation.
'Record numbers of stranded holidaymakers fill airports...' (OP1)
the use of hosepipes had been banned due to drought (OP1)
Hard candy pieces, usually flavoured with peppermint and recognisable by their black and white stripes. They are often round-ended but can be seen as angular lumps. The origin of humbug is unknown. The word also means deceptive talk, an impostor or a hoax.