Artefacts come in all shapes and sizes and are typically very rare and very valuable. Many of the members of the Majestic Few will want you to obtain artefacts from the trials, in return for favour and even powerful rewards.
Some artefacts can help you learn particularly rare spells or provide useful passive 'buffs' when in your possession. This will leave you with difficult choices to make about whether to hand over artefacts you find or keep them for yourself.
Charms
Charms come in all shapes and sizes and are often collected by even those who can't make use of their magical properties, which is to summon creatures. This always destroys, or consumes the charm, however. Charms that aren't used in a trial can be 'reverse-engineered' after victory in a trial in order to add the related summons spell yo your library.
Gems
Gems are a very common item but many of them serve no magical purpose, although they can be valuable and provide you yummy XP to improve your abilities after a trial. However, some gems contain a magic curse, which a Wizard can use. Using the curse destroys the gem. Such gems that aren't used in a trial can be 'reverse-engineered' after victory in a trial, in order to add the related curse to your library.
Not So Magic Stuff
There's lots of items to be found in the trials that aren't magical but still have value. Many can be 'traded-in' for XP after a successful trial, in order to improve your abilities. Gold-coins are a common example.
One particular item to look out for is the good old key. There's plenty of locked doors and containers that need them, with some tasty loot (and sometimes less tasty danger) to be found behind or in them.
Some of the more fiendish trials also have the exit portal appear behind a locked door. Now you know. Blame Sykes for that one. All the other Majestic Few do.
Potions
Potions come in many yummy flavours, containing only natural ingredients and no artificial sweetners. Consuming a potion provides the benefits of an enchantment to the consumer, but not to any allies in adjacent tiles (unlike an enchantment cast from your spellbook). Acid reflux is not caused by potions.
Potions not used in a trial can be 'reverse-engineered' after victory in a trial, adding the related enchantment to your library.
Scrolls
The ubiquitous scroll cannot be used by anyone other than an experienced Wizard. Recorded on the scroll is a single use of a spell that can be cast at any target that can be seen (a ranged spell). Once the spell is cast the scroll becomes scrap parchment.
Scrolls that aren't used in a trial can be 'reverse-engineered' after victory in a trial, in order to add the spell recorded on the scroll to your library.
Artefacts...