Anything that's 'this year's must have' fad - crazy expensive, rarely has any play value and headed for landfill
Baby dolls that cry, tell you they love you, wet themselves etc. What's wrong with an ordinary doll and you know, imagination?
Anything focusing on poo/snot/farts/pants etc. Because why would you want that in your house?
Craft sets. I can't stand all those make your own soap/photo frame/Christmas cracker/candle/chocolate coin type things. Ditto science kits. They get shoved to the back of a cupboard and if ever remembered, don't come out like the picture on the front. In my experience kids would prefer the same money spent on Playmobil.
Character anything. Very limited play value, and grown out of within a couple of months.
Cuddly toys. Honestly aren't we all drowning in them already? Do they really need yet another? Either they love the ones they have in which case, great, they can keep playing with them, or they don't, in which case why waste money on yet another?
Check reviews on everything before you buy. If it's heavily reduced in a toy shop, there's probably a reason! Check the Amazon reviews on it before purchasing. Also don't buy 'stuff' just for the sake of it. Better 10 things that will really be loved and played with long term, than 100 things that overwhelm the child/break/get forgotten/are disappointing/are fads/have no real play value etc etc.