The one I'm most familiar with isn't listed there, and that's the one that says it's the day when alms boxes in churches were emptied and their contents distributed to the poor of the parish.
I was always told it was the day that the servants in big houses had their Christmas and received their boxes 'gifts' from their employers. The servants obiously had to serve Christmas to their masters before having their own Christmas and I believe the 'masters' delivered the boxes and provided christmas for their servants on 26th.