As for my part-time gigs, the best thing I like about them is that I enjoy doing them (so it's not really a job) and it gives me extra cash while not having to abandon my mommy duties at home (my singing gigs are on the weekends usually and my translation/consultation work is via emails, paid online too).
The best thing about my job is the balance between interaction and alone-time. If I'm on tills then time passes quickly cos the customers are usually quite nice, but also if I'm doing shelves then I can just be by myself for a while and day-dream
Actually the best thing is probably that I don't work long hours. Only 5 at a time. And it's evening shift so it's not as busy.