When travelling around the world you need to keep in mind that you will not need fifteen pairs of shoes, a hairdryer, tubs full of gel and a suitcase full of toiletries. The necessities perhaps, but you are seriously going to have to be ruthless when packing for the travels of a lifetime. Remember you are the one who is going to have to lug your bags all over the world, so pack lightly and bear in mind you are going to have to get all of your luggage home again afterwards.
You will need to start off with your bag size. Realistically, you will need to think of just what you can carry. It will need to be lightweight and - more importantly - easy to carry. Generally speaking, most people get backpacks because they are easy to carry and will spread the weight evenly on your shoulders. If you are traveling the world then planning for the weather would mean plan for every occasion from the blistering hot to the numbing cold. It would also be a good idea to ensure that your clothing goes with more than one pair of trousers. Seriously, this isn't a fashion show, and you won't get snapped wearing the same top more than once by the fashion police, promise! Your most important clothing will be your underwear, so pack plenty. Socks are also an important factor for you to pack. Relying on your feet to walk many miles will mean that socks and footwear must be at the top of your list. You will need two pairs of comfortable walking shoes, swapping them regularly in case they get wet or if you simply hurt your feet.
When packing, you are going to have to think logically in order to save as much room as possible. Roll underwear into shoes, pack things within things like those Russian nesting dolls to create more space for all of your much-needed belongings. Your toiletries are going to have to go into the same bag, so if there are things you won't need for your trips, make sure you leave them at home. You will also need your hand luggage, think carefully about what you may need in your hand luggage. Once you get onto your plane, it won't be that easy to simply fish out necessities when you need them. In your hand luggage, be sure to pack your hand lotion, (sun)glasses, water, toothbrush, hair brush, change of underwear, medicine, wallet and valuables (all just in case). All of those important IDs will need to be kept in a VIP (very important place) these include your passport, driving license, credit cards and money. Keep photo copies of your important documents in another place, it may also be worth your while keeping all copies on a USB as well (remember you should be preparing for every scenario).