When you hike you wear hiking socks so when you try on hiking boots you should wear hiking socks. If you do try the boots on with light cotton socks you will pay for it later while you ron the trails. There are two different types of packs. You can either have an external back or an internal pack. They are both basically the same but external packs have the metal bars, the support of the bag, on the outside of the bag.
Internal packs have the bars enclosed inside the material.
So, what's the difference you ask. Well, the difference is that the external packs tend to make for easier packing of equipment. They tend to have a few more pockets. But, the internal packs on the other hand seem to be much more comfortable. This is a huge plus for long days of hiking.