“Sa Shi Su Se So” is to refer to 5 fundamental ingredients in Japanese cuisine, and I always have these. I think almost all Japanese family whose main diet is Japanese have them too as these are very often used.
“Sa” = ‘Sato’ meaning sugar
“Shi” = ‘Shio’ meaning salt
“Su” = ‘Su’ meaning vinegar
“Se” = ‘Sho-yu’ meaning soy sauce
“So’ = ‘Miso’
Also, the order of these is very important. Although it is rare to use all 5 ingredients in one dish, but there are many dishes needing 2 or 3 of them. In that case, add the ingredients with the order from the top. Sugar needs more time to go inside of the other ingredients such as vegetable, fish or meat, and if you add salt before sugar, salt disturbs the sugar absorbed in the other ingredients accordingly. Sugar also works to soften the ingredients. Vinegar should be after sugar and salt as it gets evaporated and loose the sourness if it is cooked too long. Soy sauce and miso are the last ones as they are mostly for the flavor.
On top of these 5 ingredients, I always have Sake and Mirin as I use them very often. If you use Sake or Mirin, I recommend to use them at the beginning, even before sugar in particular if you cook meat or fish as they remove the smell.