With the BH1750FVI can be measured the illuminance in lux at a point. Areas of application are, for example, photography, automatic switching of lamps for lighting at night or dusk and much more.
The DHT11 is a simple and inexpensive temperature and humidity sensor, which is ideal for small projects with the Arduino, in which it does not depend on a high degree of accuracy of the measurements. It should be used for indoor measurements.
The GY-65 is a simple breakout board for Bosch BMP085 barometric pressure sensor with integrated temperature measurement. The values can be a simple used for weather forecast, more precise (GPS) navigation (level measurement, as well as vertical climb and descent).
The HC-SR04 is a very inexpensive ultrasonic range sensor. He is primarily in robotics and autonomous vehicles in use, being possible to use the sensor for example for obstacle detection, but also level indicators or motion detection are possible with this sensor.