Not mine but from Steve the great: "Always keep a litter bag in your car. It doesn't take up too much room, and if it gets full, you can just ... toss it out the window."
Sorry Stan, wet wipes were already taken. Also in my kit is a baggy with clean paper towel (many uses including toilet functions) and another baggy with a clean oily rag and thirdly a pair or two of disposable vinyl gloves.