Most experts agree taxi or rideshare drivers deserve 15 to 20 percent of the fare, depending on the service and the cleanliness of the vehicle. (Ms. Swann once rode in a rideshare car filled with dog hair and made the rare decision not to tip.)

Airport skycaps and the bell people at a hotel should get a few dollars a bag, based on service, and perhaps more if the task is onerous, like handling golf or ski bags. Valet parkers should get $2 to $5 at drop-off and pickup.

And if you only have larger bills, Ms. Swann added, it’s perfectly fine to ask for change back.

Remember the hotel housekeeper

Etiquette experts say hotel guests should leave $2 to $5 a night for the housekeeper each morning. The American Hotel & Lodging Association recommends $1 to $5 a night left daily, preferably in a marked envelope making it clear that it is intended for the housekeeper. In its tipping guide, UNITE HERE, the labor union whose members include hotel workers, suggests a minimum of $5 a day and more for suites.

Not many travelers comply.

Despite having the most physically demanding jobs in hotels with few avenues for advancement, “hotel housekeepers are some of the least-often tipped employees in the service industry,” according to Dr. Belarmino of U.N.L.V. “Unlike servers, who are often paid less than minimum wage that is then made up by tips, hotel housekeepers’ pay is not contingent upon tips. However, it is a courtesy to tip them.”

But in the age of infrequent or optional room cleaning, which has become more common since the pandemic, the guidelines get murkier. “If you stay one night or if you choose to skip housekeeping, I would recommend tipping about $5 at checkout,” Dr. Belarmino said.