A few times in the past I've done up quick spreadsheets to compare buying food vs. eating out. I'm in the same boat as a lot of others in the this thread - poor diet, long hours, fast food. I'm not going to pull stats out because they keep changing, but as general trends go:
Eating well on restaurant food is silly expensive. Noone is arguing about this.
Buying and cooking good food vs eating fast food is a close tie. I'm not a huge fan of veggies and meat/pasta is expensive to make up the bulk of your diet, so YMMV.
Buying and cooking crap food *can* be cheaper, if you're not buying microwave pizzas and burgers.
All of this is before taking into account the cost of my time. Once that's taken into account, it makes dropping through an expensive "healthy gourmet" carvery with free wifi or decent 3G coverage a hell of a lot cheaper than spending 30 mins a day preparing lunch and dinner. Eating out for lunch and dinner means no mess, I can still bring my laptop in and bill my time while I get off my feet, away from customers and enjoy food that's far better than I can cram into my schedule if I'm making it. I get to sleep an extra 30 minutes! That's worth a lot more than the money.
Everyone's scenario is different. I try to eat good food if possible and avoid the golden arches like the plague. Sometimes, though, you end up working 16 hours in a day without a break, it's midnight and they're all that's open. It beats scrambled eggs on toast. If you have a nice 9-5 job that you enjoy and can spend your weekends pursuing your shaved meat hobby, well, that's great too.
And yes, I take multivitamins to back up my highly variable & mediocre diet because it makes me feel healthier. I'm completely unworried that it might be just in my head - as long as I'm not taking relabelled rat poison and they're cheap as chips, I get a benefit out of it so they're worthwhile.