camp follower

Short definition from Wiktionary

Noun

1. 1
   A civilian who follows an army, typically a family member of a soldier or someone who provides services to the soldiers, e.g. prostitution, sale of liquor, cooking and laundry.
2. 2
   A person who provides services to those engaged in a particular endeavor.
3. 3
   One who joins a group, movement, or project without being a legitimate member; one who jumps on a bandwagon.