I created a D&D 5e module. There is an ancient vampire's tomb as the module endpoint. The tomb was opened by a random human who dug through a cave wall near a tomb the day before the players arrived. The ancient vampire that lived there made him his spawn and flew away, because there is a lot of water in the cave (to save a 1st-level party of 4 PCs from it).
The player characters could meet the wet damaged Vampire Spawn as the boss. I am not sure if they could fight it or not, because they just ignored all plot hooks about water.
If they do fight it, there should be some nice loot here, but what kind of loot could be in the ancient vampire's tomb for a 1st-level party? I realized that I just didn't think about this when I created the plot. I am even not sure that the vampire should have any loot inside his tomb except his stone coffin.
Maybe there are some common rules for such things? Or some usual approach? I really have troubles with explaining to players why there are any treasures in the vampire's tomb. On the other hand, I can't just leave them without any reward.