I think I would go for:
Shower pull switch (so you can run the wire in the ceiling)
steel bath (will probably have an earthing tag on it, if not, it will probably have steel studs or brackets welded on for the legs, so you can put the wire under a locknut (not one that might later be loosened to change the bath height)
The hot and cold water pipes (I presume the basin and the bath come off the same pipes)
toilet - no - unless you have an iron or lead soil pipe, the only metal pipe will be the cold feed, no need to bond it separately if it comes off the same pipe as the cold taps
rad / towel heater (Waterheated only) - yes, the CH pipes that feed it, assuming they are copper.
light pull switch - yes, you can run the wire in the ceiling and join to the shower switch so you only have one wire to bring down into the room
all the other circuits and pipes you find in the airing cupboard since this is within the bathroom and you do not need a tool to gain access. Modern cylinders do not have earth tags so you just bond all the pipes going in, out and past it.
If you like to bond to the pipes under the basin as well as under the bath, it will do no harm but is not required, providing the pipes are copper and permanently joined. I suppose it would be a precaution against someone later making a repair or alteration in plastic pipe.
You are not required to earth the kitchen sink and its taps any more, BUT if you have a boiler in there, it and all its pipes need to be bonded to its supply (not via a plug). This is not an electrical regulation but a Corgi or Boiler makers rule (I don't know which).
You are not required to run supplementary bonding back to the consumer unit, only to the electrical circuits within the bathroom.
