Tortimer can open a co-op shop at Harv's Island Market if you donate 100,000 bells. He (or Cornimer) gives you access to your home storage.
How to Unlock Tortimer's Home Storage Service
After you update the game to version 2.0, go to the airport on your island, tell Orville that you want to fly, and ask to go to Harv's Island. Go to the Harv's Island Market area behind Harv's house. Donate 100,000 bells to the Lloid in the upper left corner of the area, and Tortimer's home storage service will open the next day.
How to Use Tortimer's Home Storage Service
Tortimer's home storage service works just like a Storage Shed furniture item (available as a DIY and from Nook Miles redemption from the Nook Stop in Resident Services). Just talk to Tortimer and you can choose to put items into home storage or take items out of home storage.
Sometimes, instead of Tortimer, Cornimer will be running the home storage service. If so, he will give you some acorns when you first talk to him for the day. After that, you can use the home storage service as usual.