Another vote for porridge - with some fruit and optional brown sugar it can make a nice evening meal/supper too.
A nice supper on hot days - potatoes, butter, cottage cheese or quark, and salad (lettuce and tomatoes, possibly a bit of red pepper).
Jacket potatoes with cream cheese/sour cream and salad
Vegetable stew with kidney beans - freezes well too.
One thing I did last week that worked really well and was cheap too: cooked penne al dente, took it out and fried it in plenty of olive oil with a few fresh tomatoes, some herbs, some odds and ends of grated mature cheese (good way to use up the annoying last remnants of a block).
Tap water as staple drink. Almost all Germans recoil at the idea of drinking tap water, instead preferring to buy and lug crates of expensive sparkling water. I find the idea bizarre - the tap water here is perfectly good - and wonder how much we save per year.