Normally, the fewer the better but when it gets down to one character, it gets a bit odd. Interacting with the non-intelligent environment only does so much. . .
Mind you, I've written one before, and it worked, but pondering the question of whether our hero actually gets hailed on the radio and when does raise the question of whether he's really better alone.
The time I managed to make it work the point of view character was a lot more conflicted than this one. . . .