DS10 has asked for an electric guitar, nerf gun, grow your own crystal set, wood whittling knife and some clay.
DD is really hard, she turns 8 just before Christmas, and she hasn't asked for much so everything she has asked for we've got for her birthday. She loves making things and can follow quite complex instructions so I think we might go for the cyborg hand mentioned upthread, and lego chess.
As stocking fillers they'll both be getting:
Bath bombs
Shower gel
Bubble tea kits
Slushie cups
Books
Slinkies
Pokemon cards
Crystals
Card games (Zuuli and Sushi Go, I think)
Someone else asked about art supplies...
This 3D pen is awesome
https://draw3d.co.uk/products/3d-pen?gclid=CjwKCAjwp8OpBhAFEiwAG7NaEma0yOUuBQsGtosjB2lo_8EZgsCVHw1iz9uoRRPbslMrhWtBEdBaBoCDPoQAvD_BwE
Acrylic paint pens are so vibrant, especially on black paper.
And there's a book called Learn to Draw Cool Stuff, by Elizabeth H Taylor, that's been brilliant for both my DC, especially learning to shade effectively.
Big hits over the last couple of years have been:
Roller skates
Keyboard
3D pen
Gravitrax
Table top pool table
Table top air hockey
Giant jenga
Sorry that was so long - but hopefully some ideas for you there!