Tested positive Christmas morning.

[Christmassss]

I’ve stayed in since I tested positive, when will it be safe to go out and about?

The advice is to avoid people for 5 days after the day you took your test so, in your case, 1st Jan.

If you have a positive COVID-19 test result, try to stay at home and avoid contact with other people for 5 days after the day you took your test. There is different advice for children and young people aged 18 and under.
https://www.gov.uk/guidance/people-with-symptoms-of-a-respiratory-infection-including-covid-19#:~:text=If%20you%20have%20a%20positive%20COVID%2D19%20test%20result%2C%20try,people%20aged%2018%20and%20under.

It says to try and stay away from others but when I had it I went to shops (when required) wearing a mask and also wore it when taking ds to school in the car.

The guidance of 5 days is supposedly based on 80% of people being 'safe' by then but for care or nhs workers, they still advise 2 neg tests before being at work.