My fiance and I generally wing it as well. We don't plan meals at all, unless it's something we intentionally discuss wanting to try. I have a general idea of a good amount of foods we both like so I can do the grocery shopping, plus I keep "staples" like chicken breast, garlic, olive oil, soup, bread, sliced cheese, fresh veggies, and such for easy meals and improvising. Grilled cheese is our favorite "we don't feel like cooking and we're starving right now" meal. We've also designed our own chicken alfredo casserole, which turned out really great!