Hint: The Reset Surveillance Room and the Silver Shovel

Head to the city after 8 p.m. and you may just come across a surprise. Head to the right to where the cones are and one may be moved aside at random. Enter the tunnel and you'll come across Resetti himself in his den of wonders. He'll yell at you as usual and give you a Silver Shovel (which will occasionally double your money when you use it on Money Stones).

Hint: Wisp's Lamp

On some nights after 8, you may run across Wisp. A voice will talk to you when you arrive -- he's always near water. Follow its directions until you find the source of the voice, which is a ghost named Wisp. He tells you that he lost his lamp and needs you to find it (for a pretty reward, of course!) You should then meet him in the attic of your house once the lamp is found. For doing this for him, he'll grant you one wish. You can ask him to clear your town of weeds, clear your town of cockroaches, or give you a randomized item.
You may find the lamp before Wisp appears as you go about your normal wheelings and dealings. If so, you'll know he'll appear somewhere that night to claim it.

Hint: Donation Prizes

200,000 Bells - Bridge
500,000 Bells - Fountain
1,000,000 Bells - Windmill/Lighthouse
100,000,000 Bells - Green Feather
200,000,000 Bells - Blue Feather
300,000,000 Bells - Yellow Feather
400,000,000 Bells - Red Feather
500,000,000 Bells - Purple Feather
600,000,000 Bells - White Feather
700,000,000 Bells - Rainbow Feather

Unlockable: Tool Upgrades

Golden Axe - Throw an axe into the town fountain to randomly turn it golden.
Golden Fishing Rod - Catch every species of fish.
Golden Net - Catch every species of insect.
Golden Shovel - Bury a normal shovel, then dig it up a full day later.
Golden Slingshot - Knock down eight balloons to have a random chance of obtaining it from a balloon.
Golden Watering Can - Earn a "Perfect" town rating for fifteen days, then talk to Pelly at Town Hall.
Silver Axe - Throw an axe into the town fountain.
Silver Fishing Rod - Purchase from Tom Nook's store.
Silver Net - Purchase from Tom Nook's store.
Silver Shovel - Obtain from Resetti's Surveillance Center in the city.
Silver Slingshot - Purchase from Tom Nook's store.
Silver Watering Can - Purchase fifty bags of seeds from Tom Nook's store.