Can you get all items in Red Dead Redemption 2?
Solution 1:
No
Taking the information from Rockstar directly about what is included in each edition here is what you get:
Pre-order bonuses
War Horse: This handsome iron-grey-colored Ardennes War Horse can always be relied on in the heat of the battle. With greater courage and stamina than the average steed, this is a horse that knows how to keep its head under fire.
Per this link a war horse can be obtained by taming a wild horse or purchasing from an in game store so it is possible to get.
The Outlaw Survival Kit: The Outlaw Survival Kit contains a collection of key supplies for enduring the rigors of life on the frontier, including items to replenish Health, Dead Eye and more.
This appears to just be general boosts which I believe can be obtained through regular gameplay.
Digital pre-order bonuses
Cash Bonus for Red Dead Redemption 2 Story Mode: The Van der Linde gang is always looking for ways to make more money and bring in new supplies. This in-game cash bonus will give Arthur Morgan enough to buy a weapon, some food, a handful of useful items and ammunition.
Just cash so can earn that throughout the game.
Treasure Map: Secret buried treasure can be found throughout the world of Red Dead Redemption 2. This exclusive Treasure Map for Story Mode will give Arthur a head start on the hunt for hidden riches. Must pre-order by August 15, 2018.
I'm not 100% sure if you can get a treasure map in game. However, you will be able to find the treasure organically so should be easy enough.
Special edition bonuses
Bank Robbery Mission and Gang Hideout in Story Mode: Get exclusive access to a Bank Robbery Mission, in which Arthur and a couple of his fellow gang members come up with a daring plan to break in and rob the bank in the southern town of Rhodes. Elsewhere, the Del Lobos Gang has taken over a hacienda - clear this gang’s hideout and rob their stash for a lucrative take.
This is an exclusive mission so I don't think you will be able to play it without the Special or Ultimate edition though it may be released later as DLC.
Dappled Black Thoroughbred: This thoroughbred racehorse sporting a beautiful reverse-dappled black coat will keep you at the front of the pack with its exceptional speed and acceleration. You will also get the exclusive Nuevo Paraiso Saddle, handmade in dark chocolate leather with silver medallion detailing. This horse and saddle are available in Red Dead Redemption 2 Story Mode.
This item can only be gotten with the Special or Ultimate edition.
Talisman and Medallion Gameplay Bonuses: These special Story Mode items will give Arthur a helping hand whenever they are equipped. Attaching the Eagle Talon Talisman to his boot, Arthur’s environmental awareness skill will last longer. By carrying the Iguana Scale in his personal Satchel, Arthur will take less damage while riding on horseback.
I believe these are only available through the Special or Ultimate editions but they're not really game changers so it doesn't matter much.
Gameplay Boosts, Cash Bonuses & Discounts: This collection of exclusive Story Mode boosts, bonuses and discounts will help Arthur to survive out in the harsh wilderness and better provide for his gang members and their camp. The Core Stat boost benefits Arthur’s Stamina, Health and Dead Eye Cores. Earn more cash during robbery missions with the Van der Linde gang, and when hunting and selling animal carcasses. Receive discounts on all upgrades to the Van der Linde gang’s camp.
Only boosts to help you progress quicker so not a problem.
The Nuevo Paraiso Gunslinger Outfit: This exclusive Story Mode outfit for Arthur is inspired by the clothing worn by vaqueros and banditos south of the border. The outfit features a wide brimmed black cowboy hat, deep indigo coat, worn denim chaps, leather gloves and boots.
This item can only be gotten with the Special or Ultimate edition.
Free Access to Additional Weapons: A good range of weapons is essential for survival in the Old West. Get free access to three weapons at the in-game Gunsmiths in Story Mode: the robust Volcanic Pistol, devastating Pump Action Shotgun and versatile Lancaster Varmint Rifle.
I believe these items are available for anyone just those who got the Special and Ultimate edition can get them for free so use them earlier.
Ultimate edition bonuses
Bonus Outfits: Get two exclusive outfits for your online character. The Blackrose Bounty Hunter Outfit features a long oxblood-colored coat, a vest with gold pocket watch chain, and dark pants tucked into chocolate leather boots. The Copperhead Enforcer Outfit features a fur-lined saddle-brown leather waistcoat, two-tone gloves, and pinstripe black pants tucked into black leather boots.
These items can only be gotten with the Ultimate edition.
Black Chestnut Thoroughbred: Outrun the competition with this thoroughbred racehorse in a striking black chestnut coat and also receive the exclusive High Plains Cutting Saddle beautifully crafted in jet-black leather with gold metal accents. This horse and saddle are available in online.
These items can only be gotten with the Ultimate edition.
Free Access to the Survivor Camp Theme: Customize your own personal Camp in online with free access to the Survivor theme.
These items can only be gotten with the Ultimate edition.
Free Access to Additional Weapons: Get access to the Volcanic Pistol, Pump Action Shotgun and Lancaster Varmint Rifle, free of charge from Gunsmiths in online.
I believe these items are available for anyone just those who got the Special and Ultimate edition can get them for free so use them earlier.
Rank Bonuses: As a great start for all Ultimate Edition players, you can rank up faster in online, up to rank 25.
A boost so nothing game changing and can probably be bought in online anyway if one wants to.