I think the pall bearers will receive a commemorative medal of some kind.
As for what the Queen would be wearing, why not just a very elegant shroud?
An elderly gentleman I know, who used to work for an undertaker, said that when his wife died recently, he stipulated that she should be dressed in a simple, pink shroud.
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He said in his line of work, too often he had struggled dressing the deceased in clothes the family had chosen, but were not very suitable when the wearer was unable to assist the dresser
I’m sure that years ago, a simple shroud would be the usual form of attire for most people.