Working a specific area of your body requires more than just a certain diet plan. If you want to have bigger forearms, you need to work the muscles in your forearms. You can stuff your face with food to the point where you start getting fat but, I don't think that's what you mean by getting big, I hope.
The only advice I can give you is to find exercises which target the forearms and then make sure you maintain a diet which include the necessary amount of macro/micro nutrients. The general rule of thumb for growing / maintaining muscle is to have an intake of protein that is equal to your body weight, minimum. So if you weight 150lbs, you should be maintaining an intake of 150g of protein. This might apply more to bodybuilders than to regular people but again, that is just a general rule of thumb. Some people say .5g of protein per body weight is fine too. I say to let your body tell you what the right amount is and go from there. Having a protein intake that is equal to your body weight is not only hard to do using a regular diet (eating protein rich foods) but it can also be expensive. Supplements like a protein powder or protein snacks can help with this and there is nothing wrong with taking those either. Protein alone is not enough though. You want to focus on a balanced diet which includes carbohydrates, fats, fibers, etc. Contrary to what a lot of people say, fats and carbs are NOT bad for you.
Things to think about when trying out a new diet. When you wake up for work or school, set your alarm clock 30 minutes (or more) earlier then you normally wake up and start making breakfast. Cook up some eggs or something. My breakfast for example consists of 5 fried eggs with a lot of olive oil, toast, and coffee. Sometimes I'll even make a protein shake to drink before work if I feel like I'm going to work late and I'll even make a protein shake to drink later on in the day. So lets say an egg has 6g of protein. The egg breakfast alone is 30g of protein. A protein powder can have 20-25g (+/- 5g) of protein per scoop. If you make the shake with milk, that's another 8g of protein per cup. So as you can see, depending on your weight, your breakfast alone can easily consist of roughly half to 1/3 of your protein intake. You can easily add other things like toast or crackers or whatever to help with the fiber and carbs. From there, you can build on a lunch/dinner/snack plan.
I don't go to the gym so what I like to use at home for upper body workouts is a pull up bar:
http://www.walmart.com/ip/Perfect-Multi-Gym/19792716
That's the one I use. Not only can it work your arms but, it works your core and back as well. There are lots of videos which show you different pull ups for different muscles. You can also buy dumbbells or any kind of weight and do forearm exercises at your house. I wouldn't do any kind of exercise on your way to college because you don't want to start your class all sweaty and tired but you can do them on your way home if you want.
Just a couple things to think about. Stay consistent with it and I guarantee you will see results.