Do you have kids?
I burned most of my wedding stuff--it was very cathartic;)
Divorce is a loss. We grieve losses in different ways and because of different triggers. Getting out those Christmas decorations was a reminder of what was and it sparked fresh grief. There will be plenty of those triggers in the coming months and years. Take them as they come. Allow yourself to grieve that loss and let it go. Other Christmases will come and these will be what you make them.
As for what to do with wedding things: that too is entirely up to you and in your own time. You can shove the box right back into the closet and let it sit there for now. Eventually, when you reach a different place in your grief you can deal with it much better. It took me 15 years to get rid of my old wedding band set. I still have my dress but mostly because I made it and it means a lot to me despite the fact the marriage has been over for nearly 15 years now. I will probably offer it to a neice or other female family member who wants a "vintage" gown for her day.
Good luck and remember: take one day at a time. This is a process not a single event. :)