Safe bento lunch - I just want to make sure I'm doing this right

I know there are tons of helpful posts on packing a safe lunch and I've tried to read them all, however I would really appreciate some more personal help since, well, maybe I'm spoiled! To get to the point, I'm a college student, and come the start of the semester on Tuesday I will be stuck at school four days of the week for 7-12 hours depending (I finish packing my bento at 9 then hit the road to make it to class by 10, then on most days I'm at the college until 10 at night) on the day. I will not have access to a microwave or a fridge. I figure that I'll need to pack at least two bento's to keep me sustained throughout the day. Is it necessary I keep everything absolutely cold, like with an ice pack, until I eat it? I'm not really a huge fan of cold rice or tofu, or anything, (heck, I heat up fruit in the microwave before I eat it) so would it be safe to keep them at room temperature for several hours (sometimes 8)? One thought I had was that I could pack one bento, the one I eat later in the day, completely with my frozen stash like Maki's mini-meatloaves made vegetarian, rice, and frozen vegetables, perhaps it will be defrosted by the time I'm ready to chow down? Any suggestions or information would be really appreciated and I'm sorry if these are silly questions.