How Best to Improve Concentration Saves (or avoid the check all together)? [closed]

Question

As I see it there are the following options:

Character Build:

• Take a level of a class with Con save proficiency at first level.
• Ability Increase (Con).
• Diamond Soul - (14th level Monk - not really viable)
• Aura of Protection - (+Paladin's Charisma bonus, Also affects nearby allies)
• Tides of Chaos - (Advantage, Wild Magic Sorcerer ability, self only)
• Bend Luck - (+1d4, Wild Magic Sorcerer ability used on another)
• Dark One's Own Luck - (+1d10, Fiend Pact Warlock, self only)
• Portent - (Replace a bad roll, Diviner ability)
• Transmuter's Stone - (Proficiency, Transmuter ability, but you have to give up other powers)
• Inspiration - (You must have Inspiration, game mechanic)
• Lucky - (Reroll bad rolls, feat)
• Lucky - (Reroll bad rolls, 1/2ling ability)
• Resilient - (Proficiency, feat)
• War Caster - (Advantage, feat)
• Focused Conjuration - (Can't be broken, Conjuration spells only, Conjurer ability)
• Bardic Inspiration - (+1dx, Bard ability, thanks BlueMoon93)

Spells:

• Bless - (1d4 added to save, requires concentration... so defeats the purpose unless you can use it on more than one player.)
• Foresight - (advantage w/o concentration, but this is a 9th level spell)
• Gaseous Form - (advantage, requires concentration, can't cast spells - this is for skedaddlin')
• Holy Aura - (advantage, requires concentration - 8th level spell, and super costly)
• Shapechange - (Change into a creature with proficiency and even advantage with Con Saving throws - 9th level spell)

Magic Items & Boons:

• Belt Of Dwarvenkind, MANUAL OF BODILY HEALTH, Ioun Stone of Fortitude, Blessing of Health - (Increase Con by 2)
• Amulet of Health - (Con is set to 19)
• Holy Avenger, CANDLE OF INVOCATION - (Advantage - while in effect)
• Cloak of Protection, Luck Blade (also reroll), Stone of Good Luck, Ring of Protection, Robe of Stars, Rod of Alertness - (+1 bonus)
• Staff of Power - (+2 bonus)

Other Options

• Don't get hit! - High AC, or non concentration spells that mess with getting hit (mage armor, mirror image, feats to wear armor, levels of Cleric/Fighter), Up your Dex
• Use Cover - Thanks BlueMoon93 & nitsua60
• Don't be seen - Invisibility, Illusions, get stealth skills.
• Get out of combat - Mist Step, Dimension Door
• Go Prone against Ranged attacks - thanks BlueMoon93 & nitsua60
• Warding Flare (Light Domain Cleric)
• Defensive Duelist feat (finesse weapon required)

Controversial or Edge Cases

• Temp hit points
• Make potions for spells that require concentration.

Are there other options that I have missed?

There are not a lot of ways to get to the concentration saving throw buffed. Which is to be expected in 5e, but I am tired of losing a spell first or second round, so I am trying to build up a list of tactics / ideas on how best to hold onto that 5th level spell I just cast.

Answer 1

You forgot (at least) four! Bardic Inspiration:

Once within the next 10 minutes, the creature can roll the die and add the number rolled to one ability check, attack roll, or saving throw it makes.

You can also complement the Dont get seen/hit sections!

• Stealth. Hide somewhere to avoid detection and be harder to target.

• If attackers are ranged, drop Prone. Ranged attacks against you have disadvantage. This is a big no-no against melee enemies, which get advantage. (thanks to nitsua60)

• Use cover. Run behind a wall, or inside a box, for full cover. Even standing just behind a brick fence gives you semi-cover and a buff to AC. (thanks to nitsua60)