Backpack
Don’t take the smallest, you may need some extra space later. It is better to put everything that is outside inside. The backpack of the capacity of 75l should be enough. Don’t buy the cheapest because the expensive one will really pay off. The cheaper ones are usually very uncomfortable to carry and they don’t last long. The quality ones last for years. Choose the backpack which is not too wide (it shouldn’t be broader than your shoulders) or you will have problems to break through the crowd.

I use a backpack of 55l or 60l and it suits me (I hang my sleeping bag on it). I like it because of many pockets and various belts where I can put any extra luggage. It doesn’t have the metal frame like old backpacks. It only has two metal ribbons that can be drawn in vertically. You can easily draw them out if you need to, and roll the backpack into a ball. It’s imported from China and it belongs to the group of cheap ones, but it is strong and comfortable. I paid for it 12 EUR in 1999.

Bags
It is best to sort things by their use and pack them into bags that way (one bag for utensils, another for shampoo, medicines and stuff, the third for clothes, etc.). That way you will always find what you’re looking for and your things will be dry and clean (or wet and dirty). Ordinary plastic bags could be the best solution because they are relatively strong and waterproof, they come in different sizes and you can always find another. You should take a spare one for putting off junk and dirty clothes and shoes and other stuff.

Packing
In the middle, right between your shoulders put the heavier things. Don’t pack more than 15 kg of weight. Always bear in mind that everything you packed you will have to carry plus the stuff you buy on your way (food, for example).

Bottles
Plastic bottles, Coca-Cola type, because you can always buy another when they get dirty.