In what seems like a really great sale for stocking fillers, pass the parcel gifts and a gazillion similar things, including clothes, bags and hats Alex and Alexa have a sale on right now with items starting at £1.50. If it's your first order from them, you get free delivery too, but if it's not you'll have to add £2.95 for orders under £30.
If you want Fancy Dress that's not from supermarkets, definitely have a browse there, with items from £2 too.
They also have the LEGO Friends Heartlake Juice Bar* for £17 - it seems to be upwards of £25 everywhere else right now.
Alex & Alexa specialise in kids from ages 0 to about 14, in clothes, toys, and home and nursery accessories. If you've not shopped there before, grab a coffee and start browsing. I've just lost half an hour filling my basket myself!