Chose a bag which is waterproof, durable and strong, because its going to be your companion throughout your trip.
2) Extra Bag
For your outing, where you can keep your mobile, a bottle, chargers. this is a must have because obviously you cannot carry your big travel bag.
3) Reusable Water Bottle
One of the best way to avoid plastic use while travelling.
4) Universal Travel Adaptor
If you are a frequent traveler, then this is actually one of the most important thing you should carry.
5) Passport and Visas
Without these two your international trip is not even possible. Be very careful while packing.
6) Travel Insurance
Though it is mandatory to have travel insurance in many countries, but still even if its not, it is advisable that you should have Travel insurance while travelling.
7) Medications
People often forget their medines while travelling and then it makes it difficult to find the same in another country. Make a checklist for your medicine packing.
8) Debit or Credit Card
Believe it or not, you will need it and this is one of the most common thing people forget at home while travelling.