An interstellar hitchhiker is an individual who usually travels around the galaxy by hitchhiking on interstellar ships. The hitchhiker does this by flagging down passing spacecraft with an Electronic Thumb, an electronic sub-etha signalling device. Hitchhikers can determine if there is a nearby spacecraft using the Sub-Etha Sens-O-Matic, which is a small black device that alerts hitchhikers to passing spacecraft by blinking.
Hitchhikers also carry a towel, which is about the most massively useful thing an interstellar hitchhiker can have.
Lastly, hitchhikers often carry a copy of The Hitchhiker's Guide to the Galaxy which aids them in their travels by providing information on the places they might find themselves and the things they may encounter.