Find a cool PI and do some research for him/her, seriously. I have been in two labs, one which I worked non-stop 50 hours a week during the summer, and one in which I worked a very laid back 40 hours a week. First lab was in bio and my PI stayed on top of me all day and came up with busy work if I had 10 minutes of free time. Second one was in a chem lab with an awesome PI who just cared about results, not how many hours you could work in a day. I would come in, mix some stuff up, sit around and study, go play with the mixture some more, let it react some more, blah blah blah. Needless to say, the more stressful job resulted in zero publications or acknowledgements from my PI and the less stressful job ended in me being named second author on two publications. Regardless of the job, it all depends on your boss as to how much freedom you have.