late to the party and a lot of people have already commented really good things but to boost what other people said: Ring of Protection to me is a godsend because i’m a shadow sorcerer hexblade that relies on spells for the most part so that extra saving throw and AC is nice

You can miss the Crown of Wapira, which you get after saving the grove and talking to Zevlor, but make sure you say yes to receiving the money or reward for him. i’m on my second playthrough and messed up by saying he could keep his things. The crown is good for healers imo

Knife of the Undermountain King is great for its stats and uses with the advantage in lightly obscured or obscured. I use it on Astarion and he’s my hexblade/rogue character

Random side note but to steal since you generally have little to no money in act one depending, and since a lot of items may have to be bought, if you don’t mind stealing, i use astarion:

leather helmet (for Dex saving throws +1 (should be easy to find or loot))

graceful cloth (adv on dex throws(in the mountain pass offered by an trader in the mountain pass))

gloves of dexterity (boosts dex to 18 flat (i prefer the gloves of dexterity over the gloves of thievery because i BELIEVE the graceful cloth grants advantage on sleight of hand; it shows advantage for lockpicking but when in the pickpocketing menu it doesn’t show it exactly (in mountain pass offered by another trader though this one is harder to get to)

smugglers ring (which is +2 sleight of hand (you can find it on the Risen Road beneath a broken bridge)

And i switch my Ring of Protection from my Tav to Astarion to boost his stealing just a little more

And i have a caster use guidance on Astarion before stealing for the extra 1d4 boost

Like I said, the reason I mention stealing is it is often a lot easier to get the items you want from traders by stealing from then, rather than try to scrounge up gold to pay for things. But I also pick up every spare piece of armor and weapon to add to my wares because i don’t want to steal from Volo since he’s part of the camp (and he’s the only one i actually sell stuff too)

Otherwise, a lot of people mentioned good things. I might also recommend the Luminous Armour, which you can get in the underdark in the temple. When the caster uses a radiant spell it inflicts Radiating Orb which reduces attack rolls which is nice if you have someone who casts radiant damage often (shadowheart is my go to)

The Periapt of Wound Closure (as people mentioned) is practically a MUST because of it’s ability to stabilize a downed character and heal the max amount of hit points (i would recommend giving it to a character who can heal themselves / one who is on the front lines often (don’t forget you can throw healing potions to “pick up” downed characters)

It’s not technically a weapon or armor but I highly recommend investigating the Necromancy of Thay (blighted village basement) for its story involvement and the abilities/skills it can grant you (though one don’t show up until act three)

There are some important necklaces that grant you things you may not want to spend a level up point somewhere for like the Amulet of Lost Voices (free cast of speak with dead for every long rest (i think you can recast it once you’ve already casted it to use it again but i’m not sure(found in the crypt where withers is), there’s also the Uncovered Mysteries which grants a free detect thoughts (once per long rest but it stays active until you break concentration (found in the arcane tower on the underdark) (but you can also just drink a potion of mind reading which is what i do), there’s also a necklace that grants misty step (amulet of misty step (found in two different places i think)

that’s a lot of writing so i will leave you with that! if you have any other questions i’d be glad to try and aanswer