I don't know stacks, but I've listed basic produce transported by rail in the UK here:
Intermodal / containers: EWS, GBRf, Freightliner, and fastline mostly provide container services on behalf of various internationally known shippers like P&O, Maersk, 'K' line, Medite (MSC), Safmarine and so on. On non electrified routes, it's always class 66s booked, bar Fastline which is usually class 56s. In electric areas, EWS will operate class 92s, and Freightliner use class 86s and 90s.
Oil & Petrolium: I'm not quite sure which oil companies still recieve supplies by train, think Total still do. Most is transported by EWS / Freightliner, and the former can be found using its own class 60 fleet, and sometimes 66s. FL uses 66s for these diagrams. A major terminal for these supplies is Immingham - managed by EWS.
Food: As far as I know, DRS do most of this. I reguarly see class 66/4s on refrigerator containers for Russel foods, Tesco and Morrisons. Other than that, I'm not sure.
Nuclear material: DRS move nuclear material mostly in the north-west to Sellafield, using class 20s and 37s, and sometimes 66s.
Coal: Fastline recently won a big contract to transport coal from Hatfield and Daw Mill to Ratcliffe-on-soar power station in Nottinghamshire, next to the MML, using a brand new fleet of 5 class 66s and currently 46 wagons, with the rest being hired from GBRf until they have all arrived. EWS also transport a lot of coal to Ratcliffe, in similar style wagons (though old style 2 axle hoppers can still be seen every now and then). Freightliner seem to transport a lot of coal too, but I'm unaware of where from / to. EWS coal trains are almost always class 66s (except 66001/02)
Metals: Scrap metal is often hauled by Advenza class 47s, and you can find class 60s and 66s operating on EWS steel trains from places such as Scunthorpe.
Mail & Parcels: Though largely gone, some Royal mail trains are still around, and used to be hauled up until 2003 by EWS class 73s / 90s. Nowadays, The class 325 FMUs can be found on their own, and are operated by GBRf. They currently have 86101 as a thunderbird, with 87002 likely to take over soon.
Other freight: Scrap wagons can be seen transported by Advenza freight and Cotswold rail, you can hire a locomotive for moving your scrap too. Both companies use class 47s, though the latter have decreased the number of them and are considering selling two more. Heavy plant can sometimes be moved by Colas Rail class 47s, and fastline operate some MPVs too, some of which are based at Eastcroft, Nottingham. EWS and GBRf often run infrastructure trains (new track etc) under contract from network rail, using class 60s, 66s or 73s.
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