New Mechanics and Features

DIY Crafting:

• You can now craft your own tools and items through the DIY Crafting App on the Nook Phone
• Crafting materials are gathered through various tools and means such as picking up fruit, flowers, and weeds, hitting trees and rocks with the axe, and shaking sticks out of trees
• DIY recipes can be unlocked through Nook Miles on the Nook Phone, gifting items to villagers, and unlocked when acquiring certain items such as the Manila Clam (unlocks fishing bait).

Fishing:

• You can now craft bait. So far the only bait we've seen so far can be crafted from Manila clams, which are dug up via the shovel on the beach. The DIY recipe for this bait appears to unlock upon digging up one for the first time
• Fishing was not shown in any of the videos we've seen so far (the e3 trailer shows it, but skips a few frames where the fish actually bites the bobber). This could indicate there is an entirely new way that catching a fish works once it actually bites down beyond just pressing A at the right time.

Breeding Flowers:

• Instead of picking the whole flower off the ground, the player may now only pick the flower part (stem and leaves still stay on the ground). This could indicate Pocket Camp's cross pollination mechanic is coming over (pick a flower, then use it on another flower to get random seeds).
• When picking flowers, they appear to take a few days to grow the flower part back.

Auto-save:

• The player no longer needs to save manually, as it is done automatically.
• You will no longer be able to turn off the system to reset your progress since your last save
• Since saves are fluid and automatic, presumably visiting a friend's town no longer will require all players to stop what they're doing so they can save, which will make starting up into multiplayer a lot less cumbersome than previous titles.
• Resetti is out of a job at his reset surveillance center, and now will fill a new role that is yet unknown

(Unconfirmed)

Cooking:

• There is a frying pan craftable at the beginning of the game, and a cooking pot over a fire, saucepan over an outdoor gas cooker, and a large drink dispenser are shown in the E3 trailer 
• Various food items shown or referenced
  • Coconut juice is craftable, which may be only a costmetic item
  • Upon digging up a Manila Clam, it says "I could make some amazing clam chowder with this!"

Bathing/cleaning:

• An oil-drum bathtub, clothing line, and wooden wash tub are among the very few starting DIY recipes. It is unclear whether these serve some function or are merely cosmetic (perhaps the player and their clothes get dirty over time?)