Hi K. B,
There is a "reason" why he "doesn't" want any presents... Hopefully, some day you will know "why"! But until then, I would suggest you take this "bitter-sweet" opportunity, to teach your son how sweet it is to "give" to others.
Try to be sure it's not because he thinks he's a "bad" kid. From what you wrote, I don't beleive you think he thinks that so...do take this "bitter-sweet" opportunity to let him be a "giver" this Christmas.
Honestly, it does make us feel so good when we "give" anything to others - whether it be our time, a hug, a small present, a big present, etc... When we "give", it gives us healthy endorphins - happiness. Giving actually does much more for the giver than the receiver.
I would suggest telling him that any presents he receives "he" can give (if he still wants to do so at Christmas) to less fortunate children (like may-be those in a foster care agency or Children's hosp). And, if possible, have him go with you to drop them off. He might even choose to keep some - which would be good since that would be an indication that he doesn't feel "bad" about himself or unworthy to receive gifts from others.
Also, if he does choose to give some or all of his gifts away -- ask him how it made him feel (does he miss his gifts or is he still happy about his decision because it made him feel "happiness"). Either way - this will be win-win for both of you... if not in the short term then definitely in the long term.
Keep in mind that some relatives might get mad if they find out he gave one of their gifts away - but don't worry about that or what anyone else says - Your responsibility and priority should be what is in yours and your son's best interest and those that love you should understand that.
On another note - I thought I would hate being divorced and single again - but I have come to LOVE it! I hope you do too... (that's a whole different topic - but if you're struggling with that - let me know)
I truly wish you and your son much joy, happiness and peace this Christmas and thereafter...
K. B