That depends on a lot of things. But some realistic concerns might include evesdropping using parabolic microphones, covert listening devices deployed at the meeting point etc.

Not to mention a) arranging the meeting and b) getting to the meeting need to be performed some how. Getting from point A to point B is, in today's society, not a surveillance free affair. Everything you carry can be used to track you, and even if you carry nothing, hundreds of CCTV cameras can likely follow you along the majority of your chosen route.

Thus the 'metadata' of your meeting is still known, even if the contents of your meeting isn't.