Last year DC2 was 5 and loved his Rubik's Snake - think I saw it in a toy shop but they're widely available.
Bath fizzers (he just loves bath fizzers / bath bombs - this year's are snowmen
).
We always put a comic in a stocking as it bulks it up nicely and gives them something to do early doors so they don't wake us up.
This year's stocking for him is otherwise:
satsuma
chocolate coins
glow sticks
toothbrush
Slipper socks are a great shout too. Ours have loved those in the past, especially if you can find the right character ones.