As many high-profile agencies sit idle because of the federal government shutdown, others are humming along just fine, thank you.

Many of them have escaped the fiscal ax because they pay much of their own way, or enjoy a revenue stream that's insulated from Congress.

That means the cable bill and weekly grocery ads will still fill the mailbox, due to the stamps and other items the post office sells. Social Security checks, food stamps and some other benefits will also show up on time because they are either funded with payroll taxes or otherwise deemed necessary and paid for in ways that keep them protected from lapsed budgets.

It also means applications for immigration benefits — everything from green cards to immigrants trying to change their immigration status — will still be processed.

U.S. Citizenship and Immigration Services, the arm of the Homeland Security Department that handles the administrative side of legal immigration, runs on user fees and is still handling a bevy of applications.

While most government websites are inaccessible or not being updated during the shutdown, the immigration site advises people to report for interviews and appointments as scheduled because "fee-for-service activities performed by USCIS are not affected" by the budget impasse on Capitol Hill. The only thing the agency can't do without a budget is run E-Verify, a program that lets employers check the legal work status of employees.

The Federal Reserve, the nation's central banker, is also operating as usual. The Fed not only doesn't cost the government any money, but it hands off any profits to the Treasury. The Supreme Court also will conduct normal operations until at least the end of next week.

Among other functions that remain open, all of which take in user fees or have dedicated revenue streams that don't depend on Congress:

— Passport offices run by the State Department, along with U.S. citizen services at foreign consulates. The State Department is also still accepting and processing visa applications for foreign travelers who want to visit the United States.

— The Health and Human Services Department offices that handle Medicare and Medicaid, along with the health insurance marketplaces under the new health care law.

— The Farm Credit Administration, which provides loans and other services for farmers and rural areas.

— The Federal Motor Carrier Safety Administration, which regulates truck and bus safety, and the Federal Highway Administration, which primarily directs federal highway aid to states. Both agencies are funded in large part with federal gasoline and diesel taxes, which are still available despite the government shutdown.

— The Federal Aviation Administration's airport improvements program, which mainly processes grants to airports; it operates on revenue from taxes on passengers.

— The U.S. Patent and Trademark Office is operating with fees authorized for spending in a prior year. That money is finite and may not last through an extended government shutdown.

— The Nuclear Regulatory Commission is also using "carryover" funding from previous years. The agency expects to have enough money to keep operating at least through the middle of next week.

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Associated Press writers Joan Lowy and Matthew Daly contributed to this report.

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Follow Alicia A. Caldwell on Twitter at www.twitter.com/acaldwellap