I had ... nerdy jobs.
The first was TAing for the chemistry department. I started winter quarter of my sophomore year by TAing a general chemistry class that I had taken the year before. I was responsible for my own section of 35 students, which grew to over 50 as I learned more (yay!). We'd go over difficult concepts, present practice problems for exams, hold office hours, and proctor. Pretty easy. Requirements vary from class to class (ie, some TAs graded, some didn't), you get to see a whole different side of the professor, and many depts (Bio, Chem, Physics) offer TA positions to undergrads, most of which are well paid ($13.13/hr x 10 hrs/week) This was an amazing experience, and one I was happy to repeat over and over -- twelve quarters in all.
The second (third?) were labs -- one at a lab on campus in the chemistry department (started summer after sophomore year) and one at Pfizer (started summer after junior year). It was pretty difficult juggling both labs at the same time, so I cut back on the academic one since I was getting paid considerably more ($18/hr) at Pfizer. I got the academic one by emailing the professor, and he actually trained me himself since the lab was so small. (Now they're huge and he's much busier.) Pfizer came along after I saw so many of my friends worked there, and I submitted my resume to their call for summer interns. The summer trial period went well, and I got asked to stay on for the rest of my time at UCSD. (I got to pick my replacement when I left last August -- networking works, even at the student level.) Both lab positions were invaluable in preparing me for graduate school, and the current work I'm doing for my PhD is a direct extension of the techniques I already learned at Pfizer.
So yeah, life get significantly busier if you work, but it's totally worth it, with the new stuff you get to learn, new people you meet, and who knows? You might like something so much that you decided to stick with it forever!