Onions are definitely a staple of mine. There's a nice quote by Nigella Lawson, which I am going to destroy because I can't remember it exactly, but it goes something along the lines of 'there is something so comforting about reading a recipe and the starting point being to fry some onions off.'

My other staple is spinach. Preferably fresh, but I'm not averse to the frozen stuff - for one thing it's a lot cheaper. It goes in everything. Salad, with pasta, in rice dishes, in curry, in soup.