Max gives Freak his present on Christmas Eve.  Freak and his mother, the Fair Gwen, have supper with Max and his grandparents.  After the meal, the group

sit(s) around like you do, admiring the tree and talking about how lucky we are not to be homeless, and Grim starts telling these old stories about when he was a kid and they got lumps of coal in their stockings. 

Gram has a rule the everyone can open one gift on Christmas Eve, and after Grim and Gram open their choices, Freak opens his gift from Max, which is

a gizmo that looks like a jackknife, but really it's a whole bunch of little screwdrivers and wrenches and even a little magnifying glass. 

Max thinks that Freak will no doubt be able to "invent stuff with it if he feels like it."

When it is Max's turn to open his gift, he chooses the one given to him by Freak.  In typical fashion, Freak has wrapped the package creatively, in a pyramid-shaped box that he has made himself.  The pyramid is very intricate, with directions on just how it is to be opened, and it contains a dictionary that Freak has also made, especially for Max.  Although Freak's gift to Max is much more innovative than Max's to him, it is clear that both boys have put a lot of thought into the presents each has chosen for his best friend (Chapter 15).