Weather
If the specifications of your bag do not state it is waterproof it most likely is not. You can test it yourself, but you should not test it with your gear inside the bag at a far-away country. A quality rain cover is a foolproof and cheap way to protect the contents of your bag from heavy rain or snow. No matter the location, your bag and its contents will stay nice and dry. Even if your bag is thick enough not to let rain in or you have a dry sack inside, remember: a wet bag is a heavy bag.
Size small is more than enough for carry-on sized backpacks. Don't order online, go to a hiking store and try it on your bag! |
Pickpockets
When visiting big cities, you are most likely going to use the metro. If your bag has zippers and the metro is crowded, it is not that difficult for thieves to get their hands into your bag. If you pull the rain cover over your bag before hitting crowded places, you make access to your bag very difficult. This should not cause you to disregard your surroundings, but having a peace of mind will be far easier.
Filth
Whether in the city center or hitchhiking in the outskirts, there will be dirtiness around you. When you take off your backpack and set it on the ground it may encounter dirt, water or whatever else. Often it is not as simple as just looking where you put it, because surfaces may stain or have fine construction dust on them. You can easily wash all of this off from your rain cover. With your actual backpack it gets more difficult. When you find yourself at a particularly filthy and possibly bug-infested hostel, you can put all of your belongings inside and cover the bag. The seamless design of rain cover means there is a smaller chance of bugs ending up somewhere in your belongings.
In this article, I listed 3 good reasons to own and bring a rain cover with you on your travels. If you know for a fact your bag is water resitant enough to survive rain and you do not need extra security in crowded places you could probably do without one. After all, the less stuff you need the better. However, an average rain cover weighs around 100 grams and is smaller than a fist so it is not a big deal to bring one and it can be useful in a variety of situations. A high quality rain cover will set you back about $20.