You can purchase two packs from the quartermaster when you begin the Grey Warden Joining. Once you get them, you will have 100 item spaces in your inventory. Collect everything during the main and side quests. Trade with a merchant. Continue to add more to your inventory space. A pack is 10 spaces extra, but prices tend to vary from those you buy. The quartermaster in the beginning sells them at the same price. The dwarf merchant that follows your party to camp varies. The quartermaster at The Tower of Magi has one for a heavy price, but it is worth it because you can hold more items and sell more as you see fit. By doing this you can make a lot of coin by mid-game. What you buy and sell depends on the coin you get to carry through the game.