I used to go to the gym regularly. Several years ago, for a combination of reasons, I stopped and the amount of exercise I was doing gradually declined to nothing.
I haven't returned to a gym, but have incorporated cycling into my daily life routine. During the week I cycle between 18 and 36 km most weekdays, depending on my schedule. I have been doing a combination of press-ups with various arm separation widths, sit-ups, and lifting of household objects, but with no strict routine.
I have a mostly vegetarian diet, but it is generally well balanced. I eat a lot, but my weight hasn't changed much over the past decade, even since stopping exercising. I seldom weigh myself, and have no scales, but whenever I do weigh myself it is usually pretty much the same weight. I'm not much of a fruit eater, but then again I haven't really got a taste for sweet things at all most of the time. I don't eat snacks regularly, and I don't drink much alcohol (but plenty of water).
Since starting exercising again I have seen all sorts of improvements, but my pectoral muscles, which were once fairly good, still seem flabby. I believe this is partly due to my posture, which is often criticised but causes me no pain or inconvenience, but not completely.
What can I do to firm up my pectoral muscles, preferably without any extra equipment or visits to a gym?