I agree with the basics mentioned. We live out in the country on dirt roads so for our fun walks my boy Luc is on a 30 ft long line. (Makes walks more enjoyable for both of us.) So we have a couple more commands that come in handy daily.
"Stop" He stops dead in his tracks. Use this all the time for many reasons.
"Go around" if he puts a mailbox or something between us he knows to come back the way he went and go around the mailbox. This means I don't have to walk over to whatever it was and untangle the leash.
"To the side" He moves to the very edge of the road when cars are passing.
Another thing that isn't necessarily a basic command but something I think is really handy to teach is "touch." You can use it to move your dog around, build up to other commands, and use it to teach other tricks. For example, I used touch to teach Luc "boop" and "tell me a secret." A service dog handler could use it to teach a dog to push elevator buttons or close cabinet doors. It's versatile.