Stardew Valley Luau, including the potluck soup explained

The Luau is a summer festival in Stardew Valley, which involves adding an ingredient to a potluck soup.
Like the Flower Dance before it, the Luau offers you the chance to raise your friendship levels with the people of Pelican Town. Rather than focusing on one villager in particular, however, you can increase your relations with the entire village in one single action.
Whether or not you succeed in increasing your friendship levels depends on what you contribute to the potluck; choose something awful and you'll find yourself becoming rather unpopular.

Luau date and time in Stardew Valley explained

Below you'll find everything you need to know about the Luau and its place on the Stardew Valley festival calendar:

• Date - 11th Summer
• Time - 9am to 2pm
• Location - The Beach
• Return to Farm at - 10pm
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  One of the main goals in Stardew Valley is to complete the Community Center bundles or, if you’re corporate minded, you can buy a JojaMart Membership. Fishing is a great way to earn money in Stardew Valley, especially if you decide to use crab pots and ponds. Throughout the year you’ll also be able to take in a variety of festivals, including the Egg Festival, Stardew Valley Fair and the Night Market. 

Luau and the potluck soup in Stardew Valley explained

During the Luau all of Stardew Valley comes together to cook a potluck soup, which they share with the visiting Governor.

You can add something to this potluck and, depending on what you pick, your relationships with the other townsfolk will be affected. To add your ingredient simply walk up to the cooking pot, select it and then pick your chosen ingredient from your bag.
You'll be able to judge the result of your contribution by the reaction of the Governor. If he loves or enjoys the soup, then your relations will improve with the other villagers. If he finds the soup advantage and unexciting, then all of your relationships will stay the same. If he hates the soup, however, then you'll friendship points with all of the villagers.
The items you'll want to avoid putting in the soup are:

• Anchovy
• Blackberry
• Carp
• Crocus
• Daffodil
• Field Snack
• Green Algae
• Herring
• Holly
• Joja Cola
• Pufferfish
• Red Mushroom
• Salmonberry
• Sap
• Scorpion Carp
• Sea Cucumber
• Seaweed
• Spring Onion
• Sunfish
• Sweet Pea
• Unmilled Rice
• Void Mayonnaise
• White Algae

The aim is to make a delicious soup.

If you place a certain pair of shorts in the potluck, then you'll see a unique little cutscene, which won't affect any of your friendships.
The summer in Stardew Valley continues with the Dance of the Moonlight Jellies.