I wouldn’t worry too much. The more people using it, the more likely a malicious individual is present. So a small restaurant is probably safer than an airport. If you’re logging into (or logged into) a website, be sure the URL begins with https (note the “s” and the end) so any personal data sent is encrypted. If you’re just browsing the web and not logged in anywhere, that is safe (assuming you don’t care about someone possibly knowing what sites you visited).