actually d"d "sidequests" are quests that you don't have to complete in order to beat the game, stealing money doesn't sound like a must for me
here is my sidequest idea:
as you reach some city you suddenly find yourself in the middle of a river of blood, following it outside the city the blood slowly become less seenable and at a point it begins to be simply just drops, wandering around the forest outside of town following the bloody clues you spot one of the town's guards, you then notice he got some blood covering him.
he tells you he is chasing a sick murderer, though the blood ends at that spot, you can't do much so you are forced to return with the guard to town.
back in town you will now talk to people who saw what happened, and you will also find clues around the fresh grave of a body discovered outside of town.
the clues will slowly tell you the location of an old well located around the forest.
you get inside it and you discover bones, it doesn't take you long to realize those were once humans.
you keep walking and you find the guard again, you blame him and fight him, when the guard dies you suddenly see a shadow fleeing away, you follow the shadow to an exit, you climb and find yourself in a hidden city and spot an old lady which tells you a legend about a men eaters tribe, you search for clues around the town only to discover more bones, the villagers look a bit weird and you decide it's not smart to stay, you run back down the well only to discover the guard, back on his feets , he looks hungry for your blood, you run back and you can't escape the villagers, they tell you that you look tasty, scared and confused you start begging for their mercy, it's then when someone you know shows up telling you that he/she setted you up and it was all a joke, you can then add that person to your party
it's optional cause you will have 4 without that person, i figured we can switch members in the inn or something and thus have the ability to choose the party we want