The Steam Wallet has officially been released along with the Team Fortress 2 Mann Co. Store, where players can now purchase items right within TF2.
With Steam Wallet, you can add value to your Steam account using any of the payment methods supported by Steam. Funds in your Steam Wallet may then be used to buy any item available in the Steam store on an in-game store. You can load up your Steam Wallet ahead of time, or wait until checkout. Also, different payment methods can be combined to make a single purchase.
Once you've added funds to your wallet, that money will be used by default for subsequent Steam store purchases. But if you'd prefer to reserve your wallet balance for in-game purchases of Mad Milk, Holy Mackerel and Bushwackas, no problem -- simply select another payment method during checkout. Your wallet funds will be there the next time you're ready to shop at Mann Co., or any other in-game store.