Best weapons, upgrades and mutations heavily depends on what class you're playing. Also for healing, thick smoothies or bandages should be fine
Grounded Tips

There's no defined classes, but there's technically classes. I'm not sure on the exact ones, but there's the archer (bows, crossbows and light/medium armor), the rogue (knives, swords and light armor) the tank (any weapon with a shield and heavy armor), and the mage (staffs and light armor). It's sort of defined by armor (Ex. Acorn armor increasing aggro, or Bee armor increasing bow damage)

You dont really have access to anything good until you reach the upper yard tbh

I went with a tank build when I played (Roly Poly armor, pinch whacker, Ladybird shield, security badge, meat shield, corporate kickback, reliable friend, perfect parry or smth like that, and spicy defense)
Mutation load outs
Best weapons and how to get the recipe
Best upgrades
Best healing and/or consumable and how to get the recipe