In a local shop, they have these massive jars of pre-cooked white beans, which are really great. I keep them in the fridge and when a meal could do with a bit more sustenance, I just scoop a few spoonfuls into there.

Works really well for curries and tomato sauce, but honestly, I'd have trouble naming a meal where it doesn't fit (assuming that meal doesn't already have a ton of protein). Yesterday, I did the beans on toast thing by basically just chucking beans on toast, seasoning them and then microwaving the lot. For an extremely lazy meal, that was actually quite decent.