Things US presidents can’t do in office
Drive a car on a public road - Lyndon B. Johnson was likely the last president to ever drive on a taxpayer-funded highway. However, they're allowed to drive on private property.
Use personal technology unmonitored - Presidents are now advised to restrict the use of personal technology, such as iPhones.
Accept expensive gifts -
Rules are strict when it comes to presidents accepting expensive gifts from world leaders and other dignitaries.
Use commercial airlines -
Secret Service prohibits the president to use commercial airlines. But it's a slim chance they would even choose that since they have the Air Force 1.
Copyright published works while in office - Even if a sitting US president would find the time to write and publish a book, they wouldn't have the copyright as a federal employee.
Interpret laws -
A president can have strong opinions just like any other citizen, but they can't enforce an interpretation of a law. That's the job of the Supreme Court.
Clean their office -
The president is discouraged from cleaning their office or throwing away mail.
They can't go anywhere without the "football" - The "football" is the nickname given to the briefcase the Secret Service carries when they travel with the president.
Open the windows in the White House - Secret Service requires that all the windows stay closed for security reasons. This also applies to windows in all official transportation.
Earn outside income in addition to government salary - According to the law, the president must place all investments into a blind trust until they leave office.
Make laws -
The president can't make any new laws at all, only pass a bill, or veto it. The power to create new laws fall on the Congress.
Go out for dinner -
Presidents can go out to dinner, but the Secret Service will need sufficient notice so that they will be able to secure the restaurant.
Have a normal phone call -
Secret Service is on top of everything, even when it comes to phone calls and video chatting. These can only be done on a secured line.
Provide additional funding for NASA - The president can't authorize additional funding. It all lies with Congress, especially if it's about a budget issue.
Break the law -
All laws apply to the president, and if they're broken Congress can choose to vote for impeachment.