Not edited for nontraditional/later-in-life student:
-I tutored at an on-campus tutoring center. Pay was fine (better than non-specialized on-campus work, maybe worse than off-campus would have paid but that wasn't an option for me). More importantly, I was constantly reviewing material from classes I'd already taken by tutoring them; so it helped me get more out of college. Also impressed recruiters, I think? They did only take the best students, so keep your grades up.
-Research: excellent experience in my field and preparation for grad school. Paid about same as tutoring.
-Internship: in Engineering, DEFINITELY better summer job than retail, etc. I'd stay away from the unpaid ones, though, unless that's truly a gatekeeper experience for your field, perhaps.
-Summer camp counselor: I was a bad candidate for internships between college and grad school (given the whole probably-will-never-come-work-for-you-full-time thing) and kind of burned out on staring at screens anyway. I slept under the stars 80% of the summer and went hiking, kayaking, and river rafting. Didn't pay great, but I banked it all since I had basically $0 expenses (splurged on a few more decent meals toward the end...). I did have to put up with teenagers, but most of them were a decent sort. This might be someone's version of hell but I thought it was pretty close to a vacation paying me money.