As the year goes on, if I see a great present for someone I do tend to buy it, as there is nothing worse than it being Christmas Eve and have no clue what to buy for someone!
I must admit though I find Christmas shopping quite stressful, so we often go shopping for ideas but buy most of it online now. As we don't see a lot of the family over the holiday season, if there is a family gathering later in the year the family will exchange most of their presents to save on postage, so this year we had bought most of our presents and given them by the beginning of November, it was a great relief to know that side of Christmas was practically sorted. Although we still have a few presents to buy for my side of the family.
I remember once as a young-ish child going into Leeds city centre with my mum's parents for Christmas presents, but it was certainly not a tradition as it was only done ONCE in my memory, perhaps it was a bit too stressful. My mum was very organised at buying presents throughout the year as she saw them and keeping track of what she bought for people year on year.