DS1 was the youngest for his first Christmas, he was born in November. So he got a playgym to lie under on the floor.
This year DD2 will be 5 months & will be getting a blowup pool...maybe a couple of little toys... they don't need much or care at this age which makes it so easy!
You might want to think about toys / things she will use a month or two after Christmas... at this age they are growing & developing so quickly, by Januarly your LO will be 4 months & doing a whole heap of different things to what she is now, KWIM? At that age, things they can grab onto & chew on are big winners, and DD2 has a palycentre we got off EBay (one they sit / stand in & has a tray with toys etc).
HTH