If, in the interim, you catch more bugs and fish, or discover more fossils, it's worth storing them in your home until you can donate them to Blathers - at least if you're looking to eventually complete your museum. You can see what you have and haven't donated to the Animal Crossing Bellsmuseum in your Critterpedia. Anything that has been previously donated is marked with a small owl icon.
The end of the video (first spotted by Nintendo Life) also shows all of the design tiles used to build Johto (the setting of Pokemon Gold and Silver) from scratch, though these are sadly not yet available for public use on your own Animal Crossing island at the moment.
This is hardly the first time an Animal Crossing: New Horizons player has gone the extra mile since Nintendo launched the title last month. Some have held Tom Nook's nephews hostage in an attempt to pay off their mortgage, while others have given us some of the www.lolga.com best Animal Crossing: New Horizons memes that Nook Miles can buy.