gistfile1.txt

#define BIT1 0x01
#define BIT2 0x02
#define BIT3 0x04

// ...

unsigned char value = 0;

if (flag1) {
	value += BIT1;
}

if (flag2) {
	value += BIT2;
}

if (flag3) {
	value += BIT3;
}

NSData *data = [NSData dataWithBytes:&value length:1];