I like to get a bag of Cheerios, (or the offbrand 'Scooters', lol) and add whatever dried fruits, (dates, cranberries, cherries, blueberries, raisins), and nuts, (including soynuts) I have around, making a "driver chow" that I can munch on while driving. And I've also become very fond of frozen fruit chunks, especially mango! If you happen to eat at one of the buffets, like Ryan's, you can get a styrofoam container 'to go', filling it with fresh fruit or whatever you might want later, and pay according to the weight. (Pineapple & berries don't weigh much!)
Pita pocket bread is good, you can make a pile of sandwiches when you have time, putting each in a Ziplock bag, for grabbing on the go. Add a small cup of applesauce, and it's an easy snack that won't make you feel sleepy, or overly full.
I like to keep a small half-cup container of peanut butter on the dashboard - it gets real melty in the sun, perfect for dipping crackers, pretzels, banana chunks - even dark chocolate. I haven't found a lower fat version, though.
If it's a salad I want, I throw some premixed stuff into a plastic cup, adding cherry tomatoes, feta cheese, garbanzo beans, mandarin oranges, whatever. (This part, you might want to do ahead of time, lol) In a tall cup, you can eat almost anything that you'd normally put in a bowl, while driving.
I don't know how much of this will adapt to a South Beach Diet, but it's what works for me - hope you can get some ideas.
:9
