Great subject. Now I'm on a significantly smaller income than I was I have been getting my coffee-on-the-go from Greggs. The coffee is on a par with Costa etc but importantly if you buy a coffee you can have a bacon and sausage bap for only about 20p extra! (With brown sauce if required).
Away from sausages, there's a great little greasy spoon van in Norfolk that does an amazing bacon and fried tomato bap.