Bowline, taught line and clove are my 3 go-to knots. The bowline/taught line combo for everything that I know I will need to retighten later. Clove is the go-to for fastening rope to anything and great for the cloths line. When the line stretches, just tighten it right up.
For fishing: no-name for the leader, perfect for those long heavy leaders when throwing 8Nbait, zips right through the eyes smooth as ya like. You really need to lube it up and snug appropriately though. Labrador Retriever drool is the go-to lube for that. Berkley for terminal tackle, all I ever use. I snell hooks. Kind of a hard knot to learn and trust, but once you have it down it can be done at night, in a cold, windy rain while drunk.