If I can play devils advocate here for a second... while I do think individual choice plays a big role in a lot of this, there ARE social considerations as well...
Imagine a single person, living in a... moderatley priced city or town, trying to make ends meet on their own. Now, lets take this even a step further, and suggest this person is also quite possibly still in school, trying to get their degree or next degree, because, lets face it, the job market isn't exactly overly friendly.
So maybe this person, to get by is working full time and going to school full or part time... or perhaps they are not in school but working 2 or even 3 jobs in order to pay a moderate rent, plus utilities, probably a car loan or credit card bills, gas or public transportation fees... you know the expenses of living. So this person gets up at 5:30 in the morning to get to the train or on the expressway to work, works their 9-5, commutes home, changes clothes, heads to class or the second job, and gets in at 9 or 10.
I know people who this is a reality for... and even if it's not YOU... it does happen. So yeah, the person can spend some time then preping meals, packaging them, and take them with and heat them in the company microwave if the have the option. But realistically, isn't it easeir and more convient to grab that Cereal Bar in the morning, eat some 99c value menu crap for lunch, maybe grab somthing at home between jobs/classes but more likely you are grabbing a snack when you gas up, or out of the vending machine...
Obesity is not society's fault, but in a world of rising costs, less and less time not devoted to a boss or a job, issues of most work not being a 9-5 monday thru friday issue anymore, but a 24 hour "convienence" service most places, cities like Chicago who have a higher tax on bottled water than they do on Pepsi, Choices of a 99c double bacon cheeseburger vs a 75c orange from Quickie Mart... Or for that matter a 99c GreaseBurger vs a $4.99 "healthy choice" item from the same fast food place... society isn't at fault, but it's not always 100% blameless either.