useful items primarily for no priest subclass/no pure wizard builds using item switching to prolong beneficial effect duration out of combat
( strand of favor, cabalist's gambeson arcane extension, ooblit pet...), please add to the list if you find relevant missing things.
Note: I've just discovered so far the faster way to prolong the effects in my experience: if you have both strand of favor and cabalist's gambeson, equip both of them, than place an armor and a necklace in player inventory, click e.g. the necklace, hover on the armor (or vice-versa), double click; this way one double click will swap both necklace and armor slots, doubling the swap speed
Note: a way to trigger watcher blooded state out of combat is using double necklace of fireballs on self, just pay attention when Vela is moving around (you can have double necklace of fireballs from dunnage+neketaka vendors so you can use it soon with cabalist's gambeson from arkemyr's vault). You can use also double Missile Gloves (Crookspur + Deck of Many Things vendors), but those may come later depending on your path
any unguent can be easily prolonged for +2 skill
Arcanist's Balm (+2 Alchemy, +2 Arcana, +2 Explosives)
Blessed Incense (+2 History, +2 Insight, +2 Metaphysics, +2 Religion)
Oil of Allure (+2 Bluff, +2 Diplomacy, +2 Intimidate, +2 Streetwise)
Thief's Putty (+2 Mechanics, +2 Sleight of Hand, +2 Stealth)
Unguent of Animalism (+2 Athletics, +2 Survival)
Antidote Immunity to Poison attacks for 30 sec
Aply the drug, prolong a little bit, save, reload.
Just be sure to apply Deadeye LAST as it seems to be the one giving problems to the rest.
Coral Snuff (+10% Action Speed, +5 Deflection, +5 Reflex for 180 sec)
Mouth Char (-5% Damage taken, +15% Damage with weapons for 180 sec)
Ripple Sponge (+3 Perception, Resolve, and Intellect for 180 sec)
Svef (+3 Perception, -25% Hostile effect duration, Resistance to Intellect, Perception, and Resolve afflictions for 180 sec)
Taru Turu Chew (+3 Constitution, Might, and Dexterity for 180 sec)
Whiteleaf (Concentration, +10 Will, +1 Health restored per 3 sec for 180 sec)
Deadeye (+5 Accuracy, 15% chance to Interrupt on scoring Hit for 180 sec) APPLY LAST
I think when trying the ultimate to submit it to the developers, is better not to spam save, reload (there is a chance it could be not accepted), so maybe better to apply 1 drug at a time/once before exiting the game session
Amra battle axe with Tempered Fury enchantment, Frenzy without deflection penalty, 25% chance on kill. triggers with barrels, ranger pet or blight from magran's favor belt
bardatto's luxury death and taxes: hardy on unconscious ally, not hard to trigger on combat and can be prolonged out of combat as it lasts long
bardatto's luxury grace: not sure but in theory you could be able to prolong the +3 health per 6 sec, harder though as starting duration is very low
chromoprismatic quarterstaff elemental induction (+15% Damage for 10.0 sec when hit with Acid / Fire / Frost / Electricity attacks), e.g. use necklace of fireballs to trigger
death's maw death runes? (within 5m of a killed enemy grants -15% incoming damage for 10 sec) not tested yet, may be not so easy to prolong
Death's runes can't be extended, it's a temporary aura ON the corpses, similar to cipher effects on foe
devil of caroc breastplate devil's due +2 health restored per 3.0 sec for 6.0 sec on critical hit with weapons (hit vela)
griffin's blade loyal companion: steadfast on blooded, not so easy to prolong permanently (gets overriden by spells giving the same effect) but useful as alternative to no pity for the lost watcher ability
least unstable coil Empowered Being (all lvl3 inspirations, however like all inspirations buffs if you're hit by afflictions your inspirations will degrade if you're not immune from afflictions. if you are immune it will not be overwritten unless you use it again. Also if you unequip, save, reload the buff will be saved with a different name and no more overwritten but it may weaken some effects of the inspirations like robust)
Less/Least Unstable Coil Spirit Siphon (15% action speed, stacks with Tempered Fury from Amra and Bolting Strikes from Lord Darryn's Voulge)
Lord Darryn's Voulge Bolting Strikes (10% chance on hit to get Quick for 10.0 sec, 15% Damage dealt as Shock with weapons for 10.0 sec)
Lover's Embrace dagger: Frenzy (25% action speed, -10 deflection, Strong, Fit for 15 sec) from Lover's Quarrel on female target enchant, get it by critting Vela (more safely with a shield equipped)
necklace of the harvest moon midnight wish??? (Friendly AoE: +8 health, +10 defenses for 15.0 sec per 3.0 sec, not tested yet but I doubt it works)
necklace of the harvest moon yearly reap -5% Recovery Time for 6.0 sec on crit), hit vela with blunderbuss
protective eothasian charm darkest before dawn (+5 health per 3.0 sec over 12 sec, damage reduced by -25% for 12 sec on near death), risky but good to prolong, you need to sleep once to recharge it though)
resounding call call to arms (Destroying a destructible grants tenacious 12.0 sec), not super easy to prolong but doable and definitely great to have
scordeo's edge adaptive (+2 Accuracy with all weapons for 30.0 sec on scoring Hit, stacks 10 times, easy to prolong as long lasting, stacks with blade cascade/highwayman)
scordeo's edge blade cascade (ignore recovery for 5.0 sec on scoring hit, use it on vela)
Scordeo's Edge Highwayman (20acc with ranged weapons)
scordeo's trophy opening barrage (unlimited stacking -5% recovery time), you can get very good recovery time just with this one before getting scordeo's edge
serpent crown serpent's strike +10 Accuracy (maybe also -25% Recovery Time?) for 15s when critically hit
Slippers of the Assassin Boots Shadow Form (invisible on kill, trigger it killing barrels. Reported working (thanks Raven Darkholme) with double clicking slippers from player inventory too, but so far not working this way for Kaylon and me so it may be related to specific build/setup)
[EDIT] ok confirmed I managed to get it working after save/reload: on reload you look transparent but the Shadow Form is no more working until you double click the slippers from player inventory, then it is applied again but you need to prolong it from scratch in my experience so it may be a little tedious but working
The Maker's Own Power belt reforge the flesh 10hp/3sec -85% dmg, paralyze can be worked around (blade cascade on, trigger reforge and extend it, if you knocked yourself out you will stand up and won't be paralyzed, you may still need to switch weapon, save, reload and switch weapon again to get rid of paralyze)
unstable soul essence bomb (+6 Health Restored per 6.0 sec for 12.0 sec)
wahai poraga at blades reach -20% Melee Damage Received for 2.0 sec on launching attack (hit vela)
weyc's wand attuned channel (after empowering an ability, gain +3 Power Level for 20 sec, confirmed)
Whispers from the Depths Grasping Mysteries: 30% chance on scoring Kill to gain Acute (+5 Intellect, +1 All Power Levels) for 8.0 sec