Besides worry about what clothes to take ** – being that carry on and other luggage is now severely limited – the most important item when traveling is still the passport. Without passport you cannot get anywhere easily. Example of compromised passport: During the sixties we spent each summer vacation in Italy with the family. Once while boating on the Garda Lake, Northern Italy, my friend lost his passport in the lake – slipped out of his back pocket together with wallet and drivers license. Difficult situation to resolve, there was no proof of passport documention. I personally always take with me a copy of my passport (outside pages, couple of inside pages with picture). Not that I have lost my passport, but I have used the copied pages many times, when in certain countries where even a passport is required to get some foreign currency in a bank. The copy of my passport was accepted.
Credit cards. I also always take copies of my cards with me, in case of loss or theft, for proof at a Bank or Police.
The other important gadget is a small LED flashlight. Also needed many times when in a country where power outages occur. Especially couple times in Mexico, where night comes early and fast. Besides that, also a small radio. Usually I buy a new one in any of the continents I travel, because those do not last long. Good for local news and keeping up with the language of that particular country. OTHER gadgets I always take: Mini KC Pro travel tool kit; my Swiss Army knife; mini (credit card size) OptiCard (magnifier/light)  [some items go into check-in luggage].

CLOTHING. When leaving Canada it it always cold, and therefore  when leaving I wear multiple layers of clothing, that I need again when returning to Canada. No need to pack in any suit case.
** clothes – easily can be bought anywhere in the world in second-hand stores