Simple diet/exercise plan for a busy college student?

I go to school from early morning until 3:30PM five days per week and I work 3–4 nights per week. I don’t have the time or money for a gym membership, and my food options are pretty narrow because I’m on the go so much. So, I’m just looking for some input on what I can do realistically.

Goal: Going from 135lbs to 125lbs before May 6, 2011 (my wedding date).

**FOOD**
-For breakfast I’ll either eat some yogurt with granola or cheerios with skim milk or something like that. This is normally around 7AM.
-Lunch is my issue. I can’t buy a “healthy lunch” on campus every day because of money issues. I don’t have access to a refrigerator or a microwave, so whatever I eat for lunch I’ll need to carry in my purse for about 5 hours without it going bad. Any ideas?
-I cook dinner every night for me and my fiance, so I normally just eat a healthy portion of whatever I cook.
-I also drink as much water as I can. Usually 4 bottles per day (equal to 8 cups). And if I snack, I’ll eat either some fruit, pretzels, nuts, etc.

**EXERCISE**
-I do a lot of walking at school. I park quite a few blocks away from campus and I would guess that I walk about 2 miles per day in this Southern heat just being at school.
-I only have access to a treadmill, 3 lb hand weights, and a big exercise ball. I’m not willing to buy more equipment.
-What is something I can do that 1) won’t take a lot of time out of my day, 2) will be effective, and 3) isn’t too complicated.

I’m not looking to get a perfect model body, but I want to get smaller and healthier and look my best before the wedding without making myself miserable with some diet/exercise program that I just don’t have time for.

Any advice/suggestions/input would be great!