I'm not eating cheap at my new job. I'm actually having a nice sandwich or a fresh rice bowl every day. My theory is that when work is tough it pays to take care of yourself. Eat well enough to keep up your strength.
So the nicest eats I'd ever make at home and bring to work were my fake Brötchen; deli meat and cheese in a sliced whole-wheat roll purchased at Acme Bread. I made them dry so they didn't get soggy before what was often a very late lunch; just a little butter in the roll.
A lot of times my standard when I was mixing sound at the Playhouse -- especially on those two-show days -- was something I picked up ages ago at Berkeley Rep; pita bread and hummus, often with an apple to go with it.
When there's no time to actually eat, the best work-with-one-hand-eat-with-the-other is the Cliff Bar. Unlike most energy bars it isn't all sugar and chocolate; the Cliff is almost as hard as Dwarven "Cram," and fills you up as well, too. They last nearly forever so you should always have one or two at the bottom of your gig bag for emergencies.
I recently found a new roll at the Bowl which is much like the whole wheat raisin roll I used to get at Acme (before they raised the price on it a bit too much for my liking). They are both filling and just sweet enough to be palatable with nothing but a little coffee or cold water. These aren't pastries, mind you; they are also solid, serious hunks of bread in the schwarzbrot mold (though nowhere near the seriousness of the latter, and very far from the tooth-breaking solidity of Dwarven Battle Bread).
Which basically segues to eating cheap abroad. My London trip typified my approach; I was at a four-star with continental breakfast, so I ate heavily in the morning, then got through a full day of walking and museums with nothing else but perhaps a cup of coffee and an apple saved from breakfast. Then evenings I'd quiet my stomach enough to make it to breakfast by making full use of the tea and biscuits room service would have left for me.
When I was staying in Montemarte I started with omelet and potatoes, then picked up Parisian street for for a late lunch/early supper; especially the Paris "gyro," a baguette slathered in red chili mustard then stuffed with sliced meats and frittes, all of it wrapped in paper and served open like an ice cream cone. For a lighter repast, crepes made in front of you at tiny crepe stands. I'd stop by the patisserie and fromagerie on the way back from breakfast to my room, and the evening meal was a light snack of bread and cheese or perhaps a little jam.
Tokyo is of course rather expensive, and I had to make do with the chillingly small "morning service" of one egg one slice of toast and a cup of coffee all for the special price of only 450 yen. The big meal of the day was -- when I remembered -- curry rice from one of those peculiar places that sell the food via vending machine token, food which is eaten standing up. But you get a lot of curry rice for a very good price.
My cheap eat at home right now is a three-day curry rice. Takes curry paste, coconut milk, tofu, canned albacore and baby corn and water chestnut and sometimes bamboo shoots so is close to ten bucks to make, but stretches to three servings, meaning I can make it one night and then just nuke the remainders for as many as two more.
Well, with luck I'll be able to spend a little more on food in the future. My boss says he'll be calling the temp agency as soon as a full month has passed (he'd do it now but is worried that it looks too weird) and upgrade me to full employee.