Do you still feel guilty going into a church for a wedding or a funeral - nope. I don't find myself in churches often but I realise that other people have Christian beliefs. I no longer subscribe to the Watchtower's 'Christendom' crap.
Can you bring yourself to celebrate birthdays or Christmas - hell yeah! Every year, I go up to the Cairngorms and visit friends and family. We celebrate xmas and see in the new year. In 2017-18 me, my cousin, my cousin's partner and his sister went to a big Scottish Hogmaney in the street. We saw in the new year with line dancing and whisky. Generally speaking, when I visit these guys, much stilton and turkey is eaten and much red wine and Scotch whisky is drunk.
Would you hesitate to accept a blood transfusion if you needed one ? - I would have no hesitation if I really needed one. I'd have no religious concerns on the matter. The only concern I might have would be that the blood has been properly screened. I don't want AIDS.
PS - I eat black pudding. It's rich but quite nice. I recommend anyone to give it a try.