Aside from what to pack your things IN, there are a few things that I have brought on my travels that are LIFESAVERS. These are items that have saved me/come in handy on each and every trip - aka not location/climate sensitive.
1 - Comfortable Shoes
I CANNOT stress this enough. DO NOT buy new shoes before you leave without walking 1+ miles in them first - AT LEAST. If you are trying to pack light - skip the heels (heels + cobblestone = sprained ankle) and only bring flip flops if you are anticipating public showers - because you WILL get a blister between your toes. Also, make sure you grab a pair with good supports, a little raise in the heel will give you better posture, and support around the heel will make sure your feet don't tire too fast. I bought a pair of Birkenstocks while in Greece and have brought them on every trip since - they are game changers. Seriously.
2 - Cross Body Bag
Whilst out strolling the beautiful towns of Italy, at any one moment you will be holding camera, navigating a map, and grabbing a drink of water. You will also need to carry around all of your other 'things' that we seem to clog up a purse with. Cross body bags give you hands free mobility and relieves some of the stress on your shoulder that other purse styles might. I have used this LeSportSac on my last two trips and LOVE it. The strap is adjustable, the top zips and there are around a thousand secret pockets inside. This is IMPORTANT. At any time it would take a pick pocketer around 2-3 un-zips to get at any important items I am carrying ($$, passport, phone). A guy tried in Barcelona, after the first zip he found my capstick - which is where I caught him. ALSO - it's waterproofish. No one wants to carry around a wet bag post- midday downpour in Thailand, amiright?!
3 - The Traveling Iron
I have used a backpack for my last few trips, but I can see this applicable to all suitcases - things just get wrinkly/musty after being worn/carted around the world. This stuff is amazing. Spray it on, use your hands to flatten your clothes and they will be wrinkle free and smell amazing. I use it for EVERYTHING...well, not to straighten my frizz ball hair I suppose...
4 - The Mobile Sleeper
When you are backpacking around a country, you need to be able to catch up on sleep whilst en-route to a new location. You also don't want to miss out on sleep throughout the night because there is a marching army outside your balcony (Looking at you Athens) or screaming bar hoppers that don't understand you have an uber early flight the next morning (Looking at you Grenada). These saved me both times. Sometimes there is a weird light shining into your hotel room - put on your shades. Weird noises? Block em out! Long bus/plane ride? Neck cramps are the wooooorst.
I got this scarf while I was in Hydra, Greece and have since brought it on all my trips. It's perfect to use to wrap your head/shoulders in a mosque/temple, to keep your shoulders warm at night, or to sit on to watch the sun set. I've also wrapped my DSLR with it when I keep it in my bag (keeps it safe/dry), used it as a blanket on flights and as a sarong at the beach! SO versatile :)
WOO! Now go book a trip :)