Certain missions will require you to consume or use certain items. These items can be found on this spreadsheet created by JamaIIama on Reddit here.
Daily missions will unlock for your character once you hit level 50.
When you complete 4, 7, and 10 daily missions, you will get a Gold Mission Complete Box. This box has a chance of giving you Onyx Crystals, Chaos Onyx Crystals, Blue Stars, and Metacells.
Completing these missions will give you consumables that you can use to get experience. These will be useful for leveling after you hit level 50. For headstart players, hold onto these exp potions for the 10th. They are also character bound, so they cannot be used for alternate characters unfortunately.
Seize the Day
Completing these missions will give you music scores and automatic vouchers (for fishing, gathering, music playing). Keep in mind that each of these vouchers get consumed as soon as you use them once.
Completing these missions will give you cosmetic voucher fragments (they are character bound and you will need 10 of them to create one usable voucher), as well as temporary name tags.
Completing these missions will give you pet related stuff (like traps to capture pets), potions/elixirs, and gem dust.
Completing these missions will give you any number of mesos from 1,000 mesos to 500,000 mesos.
Completing these missions will give you Blue Crystals, Green Crystals, Onyx Crystals, Crystal Fragments, and Rue.
Personally, I would heavily focus on completing all of the "Hoard Things" missions first everyday before trying to complete the other ones. I would also prioritize "Get Rich" and "Toughen Up" after "Hoard Things" afterwards.