Initially, get all of the free storage bags from various NPCS. They are:
Small Gem Bag (blue, cap. 6) - Fitzpat the Fence (Harbor)
Small Collectables Bag (red, cap 12) - Baudry Cartamon (Harbor)
Tiny Ingredients Bag (green, cap 12) - Felix d'Cannith (Harbor, at Marketplace entry) or Vertigo...