I'm in the same boat! I'm applying to work at a restaurant, because that's what I did during undergrad (all 4 years and some summers) and found it to have many benefits. I'll make a case for waitressing specifically just because of my personal experience. The cons are: 1. working in food service (or any form of customer service) can be very stressful, oftentimes frustrating, and if we're using an OT's perspective (or future OT I should say!) it often requires some level of physical strength and endurance; 2. your income will be almost exclusively from tips, so your pay will depend on factors like how busy the restaurant is, whether a particular customer wants to leave a good tip or not, etc. The pros are that 1. I've found that although this system of pay can be less reliable, it gives you potential to earn a lot more than many typical "student jobs" where you get minimum wage. If you work at a successful restaurant like I did, you can get upwards of $15 an hour to sometimes even $20 an hour, and you can get a lot of free or half-priced food. You get pretty much all your money in cash, and the schedule tends to be flexible so it's great for working on weekends only (think about the times that people go out to eat - Friday nights, weekend brunch, etc.). 2. waitressing was, in my experience, a very active and hands-on job that was a good distraction from school stress. It also forced me to become better at time management, multi-tasking, and communication, since you are dealing with so many types of customers of all ages and also with others on your staff (managers, hosts, cooks, etc.) - a.k.a. great preparation for a future career in OT, in my opinion.
Other options that I think would be great are babysitting/nannying, but keep in mind parents will often want someone to pick up their kids after school or take them to classes, etc. My sister is in undergrad right now and works at a preschool which she loves, but she makes less than I did as a waitress and goes there in the afternoons, which would not fit with my OT course schedule. You could offer your services as a tutor (especially if you speak a foreign language!), or a petsitter as well. Check out sites like Care.com, and the classifieds section of the newspaper as well as Facebook groups. There are also several jobs that involve working with individuals with disabilities, such as being a caregiver/aide or a direct support professional. In my senior year of college I worked as a DSP in a group home for adults with I/DDs, and they were very flexible with the schedule so I basically chose to work on just weekends as well. These types of jobs can be either through an organization or program (check out The Arch, for example), or with a particular individual or family. Since you'll be at a university, it's also worth looking into job opportunities for students, such as in research or maybe at the student store or campus gym - just know that sometimes these are reserved for work study. Finally I think there are several jobs you can do remotely or online, such as teaching English to kids abroad. I don't have experience with that at all but it's something that might work for you. Good luck!