One of the most important things of course you will do before contemplating planning an itinerary is to make sure you have a valid visa for the duration of your visit. Once that is done you can then plan your stops and buy your ticket, change your money. You will have to carry certain basic things that you will need away from home.
One of the most important things that you will have to purchase or make sure that you have is a good travel bag that can hold most of your clothes and essentials. It should be of high quality to withstand all the poor handling from baggage handlers and being thrown around; otherwise a cheap bag will just burst open. Buy a size that is big enough to hold your stuff or two bags. An over packed bag will easily get damaged. They should be wheeled and lockable or buy locks for them.
You will need a backpack or tote bag that will not be checked in for all your documents and anything else you need in-flight if you are flying. These may include medication, passports, valuables, business documents and personal care items. If you have lots of documents or items that you do not wish to check in get a back pack that can also be wheeled around. You do not want to have to lug it around the airport waiting for your connection or looking for your boarding gate. It is not very interesting.
Travel map and books are good for getting you there and pointing out interesting places to see especially if you are travelling solo than in a guided your group.
If you do not speak the language of the country invest in a small book with simple phrases in the language of your destination it may help you get out of difficult situations. If you are the type to keep a diary then get one preferable
An inflatable neck pillow is a good idea whether you are flying, car riding or using the train for head support.
A travel first aid kit is a good idea as accidents can happen anywhere and that can be very far away from a hospital or any help at all.
A water purification kit is an essential especially when travelling to developing countries; where drinkable water may be rare, and it is cheaper anyway than buying bottled water.
You will need converters and adapters for your any of your electrical appliance that you may need with you. You may also need a travel size hairdryer and curling iron depending on your style. A spot remover is a good idea to have since hotel laundry can be expensive; it will cut costs. Look for a good quality one that does not leave a ring on clothes nor damage them.