Pokémon games have had various types of cooking mechanics since Generation III, but Pokémon Scarlet & Violet have truly made food an integral part of the game. Everywhere you go you'll see food stalls and restaurants, along with places to buy ingredients for picnics.
The central aspect of picnics revolves around the making of delicious (and sometimes bizarre) sandwiches. With a wacky physics system involved, you'll be surprised how fun it can be to stack those sandwiches high!
How To Get Ingredients
When you're in a city or town, stop by one of the various ingredient shops scattered about and stock up on sandwich materials. If you don't have money, that's okay too -- out and about there are NPCs at their own picnic tables, and the first time you interact with them, they'll give you some ingredients.
Start Your Picnic
Once you have ingredients, find the perfect spot to set up your picnic. Look for somewhere flat and not too close to any other NPCs, then pull up your X menu and select "Picnic." The table will appear, and you'll toss your Pokémon out to play.
Choose Your Mode
Sidle up to the picnic table on the opposite side from the basket on the ground in order to interact with the basket on the table. Select the sandwich option, and you'll have the choice to either select a recipe, or press X to enter creative mode where you'll choose what ingredients you'll use to make your sandwich.
Make Your Sandwich
Once you've chosen a recipe, or elected not to follow one, you'll enter a mini-game where you'll build the sandwich. Start with the largest, flattest ingredients in order to make your sandwich as stable as possible. You don't want it falling over and going everywhere, because one you put the ingredient down you can pick it back up. This is where the physics system comes into play.
Enjoy!
After you've masterfully -- or clumsily -- set the top of your sandwich down and dropped in the fancy toothpick, you'll be treated to a brief cutscene, and you'll find out what Meal Powers you've gotten from the sandwich. If you followed a recipe, this information won't be a surprise, but if you went creative, it'll be great information going forward. Happy sandwich-making!