I think the key to buying non toy items is to pick a theme and build a larger present or set of items around it.
Magazine subscription to the Phoenix or similar. Also lots of subscription boxes to choose from like Kiwi which is science and engineering.
Outdoor games like a big badminton set, basketball hoop, swingball, see saw, frisbee, archery set, cricket set.
Baking things are good. For my tween in the past I've bought a chocolate fountain with a big hamper of marshmallows, chocolate, sweets, kebab sticks. Also did a baking hamper with cupcake moulds, decorations, icing bags, cake toppers, recipe book. And a slushie set with a slushie cup you put in the freezer (Argos and Asda sells them) with those syrups you buy at B&M. I put them together in big boxes with cellophane and tissue paper to make them look exciting as a 'set'. You could also do a popcorn machine with those striped popcorn boxes, flavoured sprinkles etc.
Things for their rooms, light boxes, fairy lights, Bluetooth speaker, flashing disco lights, projector, stars that stick on the ceiling, fold out chair bed for sleepovers in each others rooms.
Mini Instax or Polaroid type camera, there are loads of versions some come with a mini black and white printer. For your 5 year old my two loved their VTech Kidizoom cameras at that age. Could include a homemade voucher to take them for a special day out to seaside or countryside for a day of photography together and make up a photo book of your best shots.
A 'sleepover kit' including sleeping bag, a little overnight suitcase or holdall, eye mask, wash bag filled with mini toiletries and new pj to use in Brownie pack holidays, sleepovers or school residential.
Art and craft sets.