It probably goes without saying these days there are a few things that we simply need to have with us when we travel. I have neglected to bring these items with me on a number of occassions and always end up buying them again. Now I have multiples of all of them because of my own forgetfulness. These days, long before I depart I make a list of things that I must not forget and these three items are always on that list.
These days our phones have become our lifelines and although I don't necessarily like that we have transitioned to this point in time because it doesn't feel like near as much of an adventure, there are a lot of things that you simply can not do without technology these days and many places, even budget guesthouses have an almost entirely electronic booking system that you have to participate in to stay there. As odd as it sounds, I was once at a guesthouse in Laos with a dead battery and I couldn't pay with cash, they didn't accept it. So i had to sit down and wait for my phone to charge, book the room and pay online, and then they would let me stay. It's stupid but that's the way things are now.
Also, map programs are far better than a paper map or simply wandering around until you find something. It's less of an adventure but you aren't going to get lost even though sometimes getting lost ends up being the best adventure of all.
Anyway, despite my feelings of nostaligia about the "good ol' days" of travel, modern times require technology and a good power bank is essential these days. While there are lots of good brands out there I prefer the UNIQ brand 8000 mAH. It has 3 ports, can do both Apple and Android sockets, and it charges my phone 6 times on one full battery. I've had mine for nearly 5 years with no issues.
I don't know how many times I have forgotten to pack one of these only to be faced with a plug that to me looks like something that you would only plug your dryer into. There are tons of types of plugs around the world and sometimes it seems to me that certain countries are just being stubborn that they won't just get on board with some sort of universal scheme. There is no difference between the current, just the way you access it.
The one pictures above is one of the best ones, and I have never encountered a plug that it wouldn't adapt to. You can pick one of these up for around $10 and I would say to skip the really cheap tiny ones because you need to keep in mind that you are plugging what is likely the most expensive things you are carrying with you into them, so this is not the place to save money.
It might seem like a silly thing to bring along but I can tell you a great way to horrify yourself if you are staying in a cheap guesthouse: Take the pillowcase off of the pillow that you are given. There is a better than average chance that you probably would rather not see the disgusting accumulation of hundreds of people's sweat that lies below.
I always put my pillowcase over their pillowcase just for an added layer of separation between me and the fluids of those who came before. It's gross, but this is part of budget travel. There is nothing under there that is going to hurt you, but it's icky. Hostels and hotels rarely wash their pillows because it is a complicated and time-consuming process.
You can also put a bunch of stuff in your pillowcase and tie it off to use as a pillow on the inevitable uncomfortable bus ride that you encounter at some point as well.
There are, of course, many other essential items for your travels, but these are the ones that I have kicked myself the most for forgetting and now they are at the top of my list when I pack. Don't make my mistakes! I already did it for you!