Most GPS, headlamp, Walkman, camera flashes, small Mag Lights, and so on can use AA batteries. Make it easy for yourself and take only one size of batteries with you on your trip. Try to stick with AA size batteries. That headlamp comes with a spare light-bulb too. It is weatherproof buy not waterproof.
Tents come in different price ranges.
Use your common sense when you want to buy a tent because you can spent a fortune if you want. The lighter the tent the more expensive it is. It works great and the quality is very good. Know what you want and know where you want to go. If you go to Africa where Cholera can be a problem use a water purifier.