Whenever a person goes to a new destination, one of the first things they need to decide is what they are going to bring. And for most people, that depends on the duration of the trip and likely how far they will be traveling.
If I go anywhere for a month or more, I often take one of my larger suitcases to minimize laundry. I figure since I am allowed to check a bag on the plane, I may as well take advantage of it. And since I usually rent a full apartment in a new location, I have room to store the suitcase.
But when you have a suitcase it’s often hard to be spontaneous. If you go sightseeing, you usually have to find some place to store your suitcase for the day. If you get on a plane, you generally have to check it as baggage and wait for it on the other side. And if you are on a subway/metro, your suitcase will generally take up quite a bit of room and you’ll have to babysit it to ensure that it doesn’t roll away every time the subway/metro moves.
That’s why for many trips traveling with a backpack might be a better option. Not only is it smaller and easier to transport, but it also is usually much easier going up and down stairs or hills when compared to a large suitcase. I also think there’s something exciting and idyllic about strapping a backpack to your back and setting off on an adventure, like Bilbo Baggins heading down the road from Bag End after his birthday party.
You’ll likely have to do more laundry with a backpack, since you’ll have fewer clothes with you. But I personally don’t mind doing laundry every few days – in many cities the search for a laundromat is a good excuse to go out and do some exploring. And often in many cities (Buenos Aires comes to mind) you can simply drop you laundry off at a laundromat (a lavadero, for example) and have them wash, dry, and fold it for you by the end of the day, typically for the price of a coffee or two back home.
If you want to take your backpack on the plane, then you should probably stick with a backpack that is 40L or smaller. While you might be able to sneak a larger one on the plane, you are tempting fate a little bit, especially with the various low-cost carriers around the world. If it’s larger than that it’s generally safer to check it in as baggage.
If you do end up checking your backpack, then you should pay special attention to any valuables that you also check in. Some of my friends have had their very expensive DSLR cameras stolen from their suitcases, so whenever possible try to carry everything important or valuable with you. I usually take a small laptop bag with me on the plane for this purpose, which counts as my ‘personal item’ for the flight. Inside is my 13” Macbook Air, my iPad Mini, and on my current trip, my Olympus OM-D Digital Camera. If you do check something that is valuable, then try to place it deep inside your backpack to make it time consuming to steal. You are generally not protecting the item from theft from a random pickpocket, but instead are protecting it from an airport baggage worker who likely doesn’t have much time to go through your entire bag and reassemble it just to get at one item.
Some people probably think it’s a bit pointless to bring a backpack if you’re not able to bring it on the plane, but I don’t think so. A backpack still has a lot of advantageous over a suitcase, even if you do end up having to check it as baggage. For my current six-week trip to New Zealand and Australia, I decided to bring a 50L backpack (which means I have to check it as baggage) with only two pairs of jeans, five shirts, and about seven pairs of underwear. I don’t mind wearing jeans more than a few days at a time, and the odd shirt can pull double duty for an extra day. That means I only need to do laundry every 5-7 days, which is actually quite easy to accomplish. Even if you have to go buy some laundry soap and do a quick wash in a bathroom sink, you can still end up with clean clothes. So don’t let the idea of having to do laundry in foreign parts of the world deter you from bringing a backpack on an adventure.
I’ve often found that when I travel with a large suitcase that I only really wear a few different outfits anyways. So while it’s nice to have lots of options, often it’s a better choice to simply downsize to a backpack. Even if you check it as baggage, it’ll still be much easier to lug around a foreign country or to store in a hostel or hotel for a few hours while you sightsee.