Cheap and little extra items which will be useful and fun rather than just extra tat might include toothbrush, book, clothes, squirty soap foam, pens/pencils/stickers, story/rhyme cd etc.
If you just want extra stuff for the sake of having extra stuff then there's lots of cheap plastic stuff if you look around. Personally I think your ds will look back at photos and think how wonderful it was because you make it a wonderful day, not because he had loads of stuff.
We have little traditions in our household which really makes it extra special and are things I never had as a child. My ds remembers these every year and it makes it part of the whole thing.
He puts his slippers at the bottom of his bed on exmas eve, and these get chocolates put in them by Santa.
He puts out his mince pie and carrot for Santa and always gets a letter of thanks back along with a foil wrapper, chewed carrot and crumbs. We don't do the sooty footprints from the chimney to the tree, but then we don't have a fire in our chimney so I don't hae any soot to hand!
We always make a decoration for the tree each year, and every year these come out and it reminds us of that year.
We also have some christmas story books which we get out every year and start reading these at bedtime for a week or so before hand, including nativity stories.
We have the Christmas cd on while we decorate the tree and in the car when we go out and sing along as loudly as we like.
We go out together and choose what pudding we will have for Christmas dinner somewhere special like m&s.
Now he's a but older we always go carol singing with the scouts.
Think about the traditions you can start now and will continue through out his life and make Christmas extra special. That will be what makes Christmas extra special for you all, not a few extra gifts under the tree. IME you always worry it will look bare under there, and it never does!