In a pinch when out of tartar sauce I’ve mixed green relish with mayo and it’s, passable.
For that matter, mayo with hot sauce and ketchup was my accompaniment to some otherwise bland pizza and tater tots this afternoon.
Microwave Hollandaise sauce. Can go wrong easily, but when I wanted it quick it works fairly well. Just have to tend the microwave every 15-20 seconds to mix it before it coagulates. But it’s done its job more than once for me.
You can make a fruit syrup that’s to die for on ice cream. It works with most fruits, but berries are great. Blackberries, raspberies, blueberries. Straw berries. Some mix of all of them. Get a pot, sort out the bad berries, cover in water and simmer until it’s mush. run it through a strainer or sieve or somethingt to clean out the worst of the mush/seads and add sugar, lemon and maybe some cinnamon to taste. while you still have mostly-liquid juice, take some out to make a corn starch slurry. mabye a tablespoon of juice and a half to a quarter for the corn starch. (this helps it become glossy.) Sugar to texture/taste, and reduce to the desired thickness.
(Yes, it’ll eventually become jam.)
Also goes great on waffles, pancakes or anything like that… cheesecake, brownies. I can think of a lot of things.