I'm not sure if these suggestions have been made before if they have then sorry.
Number 1. When you go to the supermarket most meat products are sold cling filmed and the meat sits in a plastic tray. Keep the trays. They are so useful for putting screws/nuts and bolts so you don't lose any. Or handy to put a wet paint/varnish brush on or even the end of a grease gun--saves the mess. These trays come in different sizes and some of the larger ones can slip under your engine to catch any drips during maintainance.
Number 2. When changing either fuel or oil filters then carry a supply of freezer bags onboard. Slide the bag over the filter before undoing and then any spillage/drips and filter are caught. Be careful as when the filter is free of its retaining screw its heavy and if you're not prepared then it will end up in the bilges--which of course you were trying not to do in the first place--been there, done that.
Number 3. Keep any screw top plastic pop bottles or even the milk ones. Handy to pump any dirty, oily bilge water into and saves polluting the marina or nice anchorage. Can be then taken ashore and disposed of responsibly. Also very good for oil changes.
