This has sort of been explained that they have and carry 'the kit' as it is called in Thud! The vampires have a large brim hat, sun block and an emergancey bottle of the b-vord, MY VORD YES! as Otto would say.
I think that same goes for the Trolls, the use some sort of sunblock.
Also as Terry has said about how the DW has changed that before it was an inexpirenced writer writting and things have changed, or something like that.