As is tradition, just about every retailer under the sun has their own sort of order bonus for a Pokemon game. Here's a list of what options we have.

This list primarily covers retailers in the United States. If you're familiar with something I've missed (especially retailers in other regions), please let me know and I'll try to get it added.

In the verbiage below, when I list "Single Version" I refer to either the Sword OR the Shield game. When I list "Double Pack" I refer to the special pack which contains both copies. "Either Version" means the promotion applies to both the single copy and double pack versions of the game.

All Regions

Early Purchase Incentive:

• Claim a special Meowth capable of Gigantamaxing and using a special G-Max Move. Claim via Mystery Gift before January 15th, 2020. Available in all versions.

Double Pack Bonus:

• Two codes for a special Dynamax Crystal that allow players to face Dynamax Larvitar and Dynamax Jangmo-o in special Max Raid Battles earlier than usual. Only available in the Double Pack.

United States

Amazon - Double Pack Pre-order Bonus:

• Code for an exclusive in-game Gold Studded Leather Case for your Pokémon Trainer.

Amazon - Single Version Pre-order Bonus:

• $10 Amazon Credit.

Best Buy - Double Pack Pre-order Bonus:

• Collectible coin with pre-order.

Best Buy - Either Version Pre-order Bonus:

• $10 worth of rewards points. Will stack with the Double Pack's collectible coin.

Best Buy - Either Version GCU Discount:

• Those that still have an active Gamer's Club Unlocked account can get an additional 20% off the list price in addition to all other promotions.

Gamestop - Double Pack Pre-order Bonus

• Receive a double sided wall banner.

• The single versions also have the "bonus gift" tag, but all the graphics and verbiage in the promotional material explicitly say the wall banner is for the double pack.

Pokemon Center - Double Pack Pre-order Bonus

• Plush keychains of Grookey, Scorbunny, and Sobble.

Pokemon Center - Single Version Pre-order Bonus

• Plush keychain of Grookey, Scorbunny, or Sobble (randomly chosen).

Target - Double Pack Steelbook Edition:

• Comes with a golden steelbook game case at no additional cost. This package is a separate item, NOT a gift with purchase. Must be explicitly ordered.

Walmart.com - Double Pack Bonus

• Charm keychain featuring all three starters.

• Listing specifically states this is a bonus for Walmart.com, so unsure if in-store packages will also contain the keychain.

UK

Figurine Promotion

• Pre-ordering the Double Pack from most retailers includes a free figurine of the three starters.

GAME - Pokemon Sword Pre-order Bonus

• Special steelbook case and code for in-game tracksuit cosmetic.

GAME - Pokemon Shield Pre-order Bonus

• Special steelbook case and code for in-game tracksuit cosmetic.

Amazon - Double Pack Pre-order Bonus:

• Comes with a golden steelbook game case.

Amazon - Single Version Pre-order Bonus:

• Includes codes for in-game Gold Studded Leather Case and in-game tracksuit.

Pokemon Center London - Pin Set

• Receive a set of four pin badges, depicting the three starters and pikachu.

Canada

EB Games - Double Pack Pre-order Bonus

• Golden steelbook game case.

• Double sided Wall banner

• Package with the steelbook is a separate item. You must explicitly order that version.

EB Games - Single Version Pre-order Bonus

• Double sided Wall banner

Australia

EB Games - Double Pack Pre-order Bonus

• Golden steelbook game case.

Japan

Lots of options!

Please see /u/BeardedJJoe's helpful comment.