I second pre-preparing food. Things like pasta and soups are great to make in bulk. Make 6 servings at a time and throw 5 of them in a freezer. Then when you can't make it to the supermarket or just couldn't be buggered cooking, you can reheat them.
I don't know that I'd advocate cooking just once a week, but certainly keep a decent amount of prepared food available as fallback.
If you're after protein, bean salad is pretty good. Personally I like the following:
Combine 1 (440g) tin canneloni beans and 1 (440g) tin red kidney beans (rinse the beans in a strainer under the tap first). Add juice from 1/2 a lemon. Slice up some red onion (to taste - personally I put in about 1/2 a medium onion). Add some salt if you're that way inclined (I am
). That makes 2 full meals. There's about 25g protein per serve.
It takes 5 minutes to throw together, and requires no perishable ingredients.