Belatedly catching up with the thread, was in Costco this week and lots of Christmas stuff in, although not all by a long way (including the paper which is often there in August!).
Giant dolls house with furniture - £138 (the box has Kidkraft Grand Estate Dolls House written on it)
Giant Panettone or Panettone with Tiramisu cream filling in tins - £6
Assorted nice tins of biscuits from £4 to £10
lego city advent calendar - £16.78
3 pack of hex bug robotics for £30 (seem to be sort of playmobil-ish - can only find this of them, but can't find them for sale elsewhere even using the might of google! so no idea if they are a good buy or a good thing but may well appeal if your dc like space things or building things...)
marble run - £30 - looks much better than the ones they've had the last couple of years. ds2 wanted one from 3 years ago, I went to get it and they had sold out. Have looked closely at them ever since but they haven't been anywhere as good as the first one he noticed. this isn't quite as good, but is close enough! Name on the box is Marble Mania Xcelerator - it's this one on ebay for £44
Haynes Build Your Own Jet Engine - £23 (£33 on amazon)
Big snuggly double sided fleece thows £14 (I have a couple of these I bought last year and they've worn really well - ds2 took a shine to them and has used one instead of a duvet for the last year and it still looks almost as good as new despite being hammered and washed plenty!)
Craft beer advent calendar (23 beers plus glass) £36
Also - Stikbots - not in yet this year but last year I got a set for ds with 3 stikbots, tripod and background for about £15 - it was cheaper than the set with 2 bots in from Amazon. Who knows if they will do it again this year but if you want it and go to Costco, it's worth keeping an eye out for it.