I'll start:
Creme fraiche - I buy this to go in a chicken paprika casserole thing I do, but then can't think of another way to use the other half pot within a week.
Sweetcorn - the dc like tuna sweetcorn (ick!!) in wraps and sandwiches but again I only need half a tin. So the other half festers in the back of the fridge until it grows blue mould someone realises and chucks it.
Coleslaw - never eat the whole tub
Olives - ditto
Grapes - similar
Apples - quite often the apples end up going wrinkly
Potatoes - omg, I have thrown away so many potatoes and now we have full blown potato plants growing out of our compost bin