Don't go into debt as such, but don't go mad either, and counteract the extra Christmas spending by what my mother used to call 'going on frugals' after Christmas.
Part of which includes using every scrap of leftovers, boiling up turkey carcass for stock/turkey stew, making pea and ham soup with the last shreds of gammon, etc.
Another 'frugals' ploy of my mother's was what she used to call 'dustbin soup' - i.e. whatever veggies/suitable leftovers you happen to have, plus any lentils, pearl barley, macaroni, etc. you have in the cupboard.
Luckily dh would happily eat this sort of thing every night! We usually have some grated cheese on top.
Great for veggie intake, and use of cheap, seasonal, UK veg.