Mystery Of The Stardrops

All seven Stardrops:

• Stardew Valley Fair - 2,000 star tokens at the shop (Fall 16; token-farm the games or bring a winning grange display for Blue Ribbon)
• Mines level 100 - in the chest
• Krobus's shop in the Sewers - 20,000g (Rusty Key from Gunther at 60 museum donations)
• Spouse - given at 12.5 hearts of marriage
• Old Master Cannoli in the Secret Woods - hand him a Sweet Gem Berry (grow a Rare Seed from the Travelling Cart)
• Museum - reward for 95 donations (A Complete Collection)
• Willy's mail - for completing the fish collection (Master Angler)

Each one permanently raises max energy, so grab the easy ones early rather than saving them. The museum and fishing drops are the long poles - everything else is money and calendar.