There's hardly an item on the map that doesn't have some value and you'll be able to use this fact to your advantage. The gray items could be sold for a profit and the white things are stackable and can be used for crafting. It follows that anybody will buy them if you place them up for sale at the Auction House WOW Classic TBC Gold, if the purchase price is correct. If you can not be bothered to perform auctions and you want to prevent the fees, then you may also just sell these items in the seller. Some of the items you loot increases in value over time and this is something to consider when you're handling your storage space.
In close connection with the previous point, you will not be able to carry much loot in case you don't have a lot of extra storage space available to transport these products. This will allow you to spend additional time looting and leveling and less time handling inventory and running back and forth. Bags are certainly one of the more expensive things and therefore it would be cheaper to get a tailor who will make you fit you with a new set of bags in exchange for goods, services or even a smaller price. You can also loot cloth that's a fantastic thing to hold on to.
Another method to save money is by cutting back on some of those expenses. Food and drink is going to be a number of the priciest items and till you reach level 40 you will be spending over 15 gold a soda . But, you could make great buddies with a mage who may conjure these libations to get a cost or a favor or whatever bargain you reach. Don't forget that if you go offline for more than 15 minutes conjure items will vanish.
It's a common error to sell items in the Auction house for less than their Whole value at the Vendors. This is a gold depleting trap and should be avoided like the plague buy WOW Classic Burning Crusade Gold. If you have an item and you intend to sell on the AH for just marginally more than the cost at the vendors, it would be better to just sell at the vendors and prevent the price of the AH commission if you don't create a sale.