Both my kids have on campus jobs -100% not related to need and 100% about them having more “wants” ie: fun money 
Both my kids spend very differently too - one is in an area that has a lot of off campus places to go and spend and the other one is at a remote LAC - so don’t forget about personal spending depending on the school area.
They had no issue finding work -one is a tour guide (competitive application), school phone-aton caller for alumni donations and our other child is a D1 athlete with a big training commitment and still is able to work as a disability note taker (takes notes in class for students that have accommodations) and is also a writing fellow - both these jobs vary on hours from professors and students - so her earnings change each semester.
These jobs have nothing to do with work study.