I understand how that feels. Used to bother me a lot in the beginning.
You should set some boundaries, though. He can pack his own bag. He can go buy what his son needs for his trip. He also shouldn't be returning dirty laundry. He can return it when it's clean. YOur MIL may be sweet, but sounds totally clueless.
Remember though, you take a trip with BF and son and his kid too. ANd it is great that when your son is with your ex, he's got someone around his age he is having fun with. I know it's hard to see that way, but it will help you refocus so your son doesn't get a bad feeling.
