I almost always use either parchment paper or a nonstick silicone silpat to line my baking sheets. It’s a snap to pull off a sheet and lay it on the pan, and it always saves me time on cleanup on top of preventing cookies, etc. from sticking.
When it comes to other pans – loaf pans, cake pans, pie plates – I don’t always bother trying to cut the parchment to fit perfectly into the pan. For round pans, I will usually line only the bottom with a circle of paper and, for rectangular pans, I might use aluminum foil, if anything at all.
Recently, I came across this set of pre-measured silicone pan liners that sound like a great solution. The set of three includes 9-inch round, 9×5-inch loaf and 8-inch square liners, ready to pop into your pan at a moment’s notice. The sizes won’t work for all pans, of course, but they are extremely common and very likely to come in handy. They’re reusable, nonstick and (at the moment of writing this) on sale.