Fortunately, the kit manufacturers sell a variety of wagons that are approprate for our period of the late 1950s to mid 1960s. Possibly rather venerable by this time would have been ex-NER wagons, so this example of the Wizard Models diagram B12 plate wagon has been weathered to look suitably decrepit.
One of the older models is the LMS long low currently marketed by Chivers, and formerly a Ian Kirk kit. These models are available with and without bolsters, and the picture below shows one of the ex-LMS vehicles branded Plate by BR.
One of the most widespread steel carrying wagons was the steel sided plate wagons produced by the LMS, LNER and BR. The Parkside kit is a good starting point for these, although the prospect of manufacturing a riveted version fills me with some concerns -- any ideas welcome. The picture below shows one of these kits that has been modified to model the LNER vacuum braked version.
On my workbench at the moment I have a couple of other plate wagons that will be models of the BR unfitted version with plate axleguards courtesy of a Bill Bedford chassis kit, and a later fitted version with hibox axleboxes.
Some of these plate wagons were adapted with double bolsters, and other adaptations carried trestles. The double bolsters are also catered for by Parkside. The rather grubby example below has deliberately wonky bolster uprights, but the plastic ones supplied with the kit are very fragile and need replacing with etchings at some point.
The Parkside trestle wagon is a bit of a puzzle, as it appears from photos that the BR Trestle-EA wagons modified from plate wagons had a replacement steel side rather than retaining the original plate wagon side. However, it is easy to fabricate a new side from plasticard. There are some nice pics of trestles built to run on Canada Road here and here (scroll down a bit on each page), which were an inspiration for me.
Speaking of inspiration, no blog post on modelling wagons could fail to acknowledge Paul Bartlett's wagon photos, miraculously restored. Paul, you are a star! Another massive source of insipration are of course Geoff Kent's books on the 4mm wagon.
There's lots more to write on this topic. Bogie bolsters, single bolsters, and representing steel loads all come to mind. However, it is logical to bring up the rear with some brake vans, which would also make a fascinating post of their own. Your homework is to identify which of the items in the following picture has been built from a Dapol kit, and which is the rather excellent new offering from Hornby.