I'm lucky that my work hours aren't super-rigid — as long as I get my work done and put it 8 or so hours, I'm set.

You have two choices to avoid that. First off, find out if you really have set hours at work. If you don't, come in an hour later, and eat (quickly) at your desk and just stay 10-15 minutes later in the evening.

You'll also save money from not going out in the day. A variation of this I actually do: I buy a breakfast on the way in, and take a fruit/other snack to eat midday if I get hungry.

Or you could just take the lunch and get home later (which can make you miss traffic).

Depending on where you work, you may just be able to be in the office less if you can get your work done faster. Check out Getting Things Done and other organizaation systems to see if that will net you a little more time.