Best Buy has a promo running where you get a $10 savings code for each $10 or more order you place with in store pickup (maximum three total transactions).
The orders need to be $10 or more pretax and so ideally to maximize gains you can get $10 eShop or PSN cards (cannot find physical $10 XBL card correct me if I'm wrong). With a maximum of three orders just place 3x single $10 card orders and then we all should get the credits in January and can essentially buy $30 more credit making it $60 credit for $30.
I am sure there are other good ways to use this promo but this seems ideal for most here!
*Offer valid 12/3/17–12/16/17 on BestBuy.com orders with Store Pickup items totaling $10 or more (before taxes and shipping costs). Limit of 3 qualified transactions (limit of $30 in savings codes) during the promotional period. Limit 1 savings code per customer per transaction. Valid e-mail address must be provided when ordering to receive savings code. Savings code(s) will be e-mailed starting on 1/14/18 and are valid through 2/3/18. Savings code(s) may be redeemed online or in store. Not valid if your order is canceled, your item(s) are returned, or on item(s) that are not available for Store Pickup. Products from the following brands are excluded from this Store Pickup offer: Bose®, Boston Acoustics, Breville, Electrolux, Google, Leap, Sonos, and Wacom. In addition, select televisions, sound bars and Blu-ray players from Samsung, Sony and LG, the Dyson Supersonic, select projectors, select Beats by Dr. Dre, and select headphones and portable speakers by Sony are excluded from the offer.