One of the many ways Dakota and I attempt to be both frugal and healthy is by packing our own lunches as often as possible. I think Dakota manages it more often than I, although my job involves going out to lunch several times a week, so I have an excuse. Several years ago, I came across some reusable sandwich bags and thought they were a great idea. I purchased some, and we've used them instead of disposable plastic sacks ever since.
The first variety I picked up, which we still have, are called Wrap-n-Mats. They're basically a flat rectangle with the corners cut off. One side is cloth and they other side is plastic. You place your sandwich in the center, fold the mat around it and fasten with a strip of Velcro. They work quite well, and, when you open them up, they make a nice little surface to eat off at your desk.
Recently, I picked up two other varieties of reusable sandwich bags from a website I like called reuseit.com. One was their own store brand of bag, and the other is made by LunchSkins. They're both pouch-style bags, which means they work for sandwiches, but you can also fill them with crackers or cookies or carrots.
I don't have a strong preference for any particular type of reusable sandwich bag, but I do recommend them as a great way to stop using disposables. They're not cheap, but if you use them several times a week for years, then I think they'll cost a lot less than disposable bags. Or, if you're crafty, make them yourself with some oilcloth or other water-resistant material. I've seen some really cute snack bags on various craft sites that I'll probably make for my son when he starts taking his lunch to school. All you need is a little bit of cloth and some Velcro.
Another thing I'd like to do is start taking my own containers to take-out places. We don't get take-out food that often, but when we do I always feel bad about how much plastic and--horrors!--Styrofoam is involved in packaging the food.
In case anyone is wondering, I am not getting paid for talking about these products or the website. I sometimes get those offers, but haven't taken anyone up on them so far. If I ever do get a free product, I will be sure to mention that fact in the text of the post.