Items at a glance
Buy extra space, not just a bigger number
A six-slot bag in an empty slot adds six spaces. Replacing a four-slot bag adds only two. Compare the price with the space you actually gain.
For a fresh character I would use drops and an accessible quest first. If slots remain empty, compare a crafted Linen Bag with the vendor option. Keep some money for training and travel.
Alliance: Soft Saber Pelts in Dolanaar
From level 4, Aldia in Dolanaar offers Soft Saber Pelts. Find her on Teldrassil at approximately 55.5 / 57.2, collect six Soft Nightsaber Pelts and return to her.
The reward is a six-slot bag. This is convenient while questing on Teldrassil; I would not make a long trip solely for this small bag.
Open map · Alliance · Dolanaar
Locations and coordinates
Horde: Carry Your Weight in Razor Hill
Furl Scornbrow is in the Razor Hill watchtower, approximately 49.9 / 40.4 in Durotar. From level 4, accept Carry Your Weight and collect eight Canvas Scraps.
Return them to Furl for the six-slot Handmade Leather Bag. It binds on pickup, so plan to use it on this character rather than mailing it to your bank alt.
Open map · Horde · Razor Hill
Locations and coordinates
The quick vendor alternative
The Small Brown Pouch has six slots and a base vendor price of five silver. Reputation discounts can change the price you pay. Check the same item at a general goods vendor before buying from the Auction House.
Brog Hamfist in Goldshire is one option in Elwynn Forest. For the Horde, Duokna in the Valley of Trials sells these supplies. Vendor purchase price, Auction House price and the sell price in an item tooltip are three different values.
Craft and price a Linen Bag
The six-slot Linen Bag is taught by tailoring trainers at skill 45. Each bag needs three Bolts of Linen Cloth and three Coarse Thread; making the bolts requires six Linen Cloth.
The calculator opens this exact recipe. Compare materials plus any crafting fee with the price of a finished bag. Cloth you gathered yourself still has value: you could sell it or use it for First Aid.
Actually equip the new bag
Place the new bag in an empty bag slot. Empty an old bag before replacing it. Keep the old one only if you already have a clear use for it.
A dedicated reagent bag is not an unrestricted extra backpack. Check what it accepts. Quest items, food and equipment still need suitable ordinary space.