There’s a lot of good advice in this thread. I was a … not poor, but well below the average income kid at my undergrad private school, and then I went to a large public state flagship for grad school. Here are a couple of things I’ll mention. At the private school, once tuition and room and board were paid at the beginning of the semester, there were no more hidden ‘gotcha’ fees. Clubs aside from Greek were funded by the university, there were lots of free concerts, free lectures, photocopying was covered, etc. It’s been a while now so I don’t remember all of the details but in contrast at the state school a lot of things like photocopying were extra, little things like that.
There’s a lot of talk now on campuses about increasing economic diversity and how to make sure the lower-income kids who are admitted actually graduate and some campuses are doing a better job of it than others. This isn’t just a private vs public issue… it can matter which private and which public. Some are going out of their way to have extra support staff to make sure kids like you are getting the resources you need to be successful and feel like you are a valued part of the community and whether you choose to land at a private or public college you want to check out what the graduation rate is for their lower income admits.