I don't see anything wrong with what you've got... sounds logical if you are planning on writing to the file in a stream.
If the size and availability of your data is such that you don't need to maintain an open channel to which you can stream data (which I imagine is not your case since you explicitly specified needing to create an empty file), you could eliminate the second line:
NSString *content = @"Put this in a file please.";
NSData *fileContents = [content dataUsingEncoding:NSUTF8StringEncoding];
[[NSFileManager defaultManager] createFileAtPath:@"/Some/Path/foo.txt"
contents:fileContents
attributes:nil];