Apart from all of the aeroplanes I used to make with Airfix and Revell plastic kits as a lad, I remember a few other sorts of kits with great affection.
This railcoach for instance. Dad had bought it in the early 1960s with a view to putting a small electric motor in it so we could run it on the OO-guage model railway he had built for us. No photos exist of this as far as I've been able to find anyway. It was built on four large pieces of fibreboard which slotted together to give a floor-filling layout with an oval track shape with platforms on both straight runs and twin tracks (I have a brother - it was necessary for a peaceful life for us both to be able to play at the same time!)
We each had a full size engine - his was Princess Elizabeth and mine a more American-looking affair with a huge cow catcher on the front. We each had a shunter engine too. Mine was a GWR tank engine and Frank had a diesel shunter. Between us we had a collection of rolling stock including a couple of pullman carriages, four red carriages with lights inside and a varied assortment of trucks and goods containers of one sort or another. Looking through the Internet now, it becomes obvious how many Dad had built for us out of Airfix kits. In fact all of the buildings that we had to go on the layout; platforms, stations, kiosks, houses, signal boxes etc. all came from Airfix kits.
The Railcoach however, stayed in its box, pristine and a source of never-ending anticipation for us. When would Dad finish it? When would we be able to put it on the tracks and send it whizzing round? I'm not really sure why, but it never did get built. But in truth we probably got more enjoyment over the years from opening the box and looking at all the green pieces of plastic, the set of decal transfers, the instruction sheet and - great excitement - the tiny electric motor that Dad had placed in the box, than we would have done had he built it for us to smash up in a collision with one of the metal locomotives after half an hour's play!