Similar to Blessings and Training, an Elite Membership makes the character a part of prestigious, secretive, or otherwise rarefied organization, which in turn grants them the right to acquire special training from this organization, obtaining unique abilities known only to them (as well as more mundane training if desired). Equally useful is the camaraderie and backing of this organization, which can give the character access to people and places often beyond their reach.
Generally, acquiring the unique abilities of the organization takes as long as training to learn a new language or tool proficiency (see the Player's Handbook).
Below are two example organizations. Using them as guidelines you can craft your own.
Champions of the dwarven kingdoms and among the most celebrated of their race, the Dwarven Defenders have a legacy spanning back to the most ancient memories of the dwarves. While not every hall boasts a dwarven defender, those who do sleep soundly knowing no orc or hobgoblin will get past them.
Membership. To become a dwarven defender requires a demonstration of steadfastness in the face of the enemy while defending dwarven lands or homes. In rare instances a non-dwarf is recognized as such a hero and is permitted to become a member. However, the leaders and trainers are exclusively dwarves. Fighters and paladins are most frequently admitted to the ranks of the Dwarven Defenders, though clerics, rangers, and even bards are not unheard of: those untrained in the use of armor are not permitted, however.
Unique Abilities. Having been sworn to the fellowship, a Dwarven Defender can be trained in the following abilities.
Durable. You gain 2d12 hit dice, adding them and your Constitution modifier x2 to your total hit points as normal. This does not affect your level in any way, but in all other respects it behaves as normal hit dice. You must be at least 10th level to successfully receive this training.
Defensive Stance The Dwarven Defender plants themselves in place, becoming like an impenetrable fortress. On your turn, you can enter a defensive stance as a bonus action. While in the defensive stance you gain the following benefits if you are wearing armor or using a shield:
*You have advantage on Strength and Constitution checks and Strength and Constitution saving throws.
*When you make a melee weapon attack using Strength, you gain +2 bonus damage.
*You have resistance to bludgeoning, piercing, and slashing damage.
*Attack rolls made against you have disadvantage.
The defensive stance requires utmost concentration: while spells can be cast while in a defensive stance, they cannot be concentrated on.
Your defensive stance lasts 1 minute. It ends early if you are knocked unconscious or you move, on your own or by another creature's actions, more than five feet in a round (if he is in a moving vehicle treat the space within the vehicle as unmoving to determine if the stance ends). You cannot enter a defensive stance while using rage or a similar ability.
After entering a defensive stance, you must complete a long rest to use it again. At 10th level or higher, you can receive additional training, allowing you to enter the stance up to three times before needing a long rest.
Once exclusively high elves, the Arcane Archers combine their magical affinity with the extensive training every elf receives with both the longbow and shortbow. In time it eventually spread to the other subraces, half-elves, and in this day other races too may learn the secrets if they prove themselves worthy.
Membership. In addition to the absolute prerequisites of proficiency with the longbow and/or shortbow and the ability to cast at least one arcane cantrip and one arcane spell of 1st level, the prospective member must also have made an exceptional impression upon the elf who will become their sponsor. While other races are now permitted to learn these secrets, only high elves may take on students and pass these secrets on.
Unique Abilities. Having been accepted by a teacher, an Arcane Archer can be trained in the following abilities.
Magic Arrows As a bonus action, before making any attacks, you can imbue your longbow or shortbow with a spark of arcane energy. Until the beginning of your next turn, any arrow fired from this bow is a magic weapon attack and has a +1 bonus to attack and damage rolls. This bonus stacks with other enhancements, should the bow or arrows already be enchanted.
Distant Cast As an action, you can imbue one of your arrows with a cantrip, and can then fire this arrow as a bonus action. You can then immediately cast this cantrip from the arrow, treating where the arrow landed as your location to determine range and line of effect and the like. If the arrow hit a creature, you can use it to deliver a cantrip with a range of touch.