Protection is important.

Buy card sleeves, deck boxes, and binders.

Yokai Watch cards are considered "standard size" trading cards.

A fan favorite for card sleeves is Dragon Shields.

A hundred (very durable) sleeves for about $10.

My personal favorite cheap deck box is Legion, which can store 100 cards. And, it comes with a divider so you can store two decks in one box.

Playmats are more subjective. They are meant to give a clean gaming surface. You can get ones with art, or basic color ones.

They also can provide a soft surface for flipping your medals. Most are like a giant mouse pad, and are machine washable. (But not all!)

Dice can be handy, but I don't see much use for them in this game.

Just make sure to take care of your cards.

Edit: "Standard sized" means /r/magictcg and /r/pokemontcg sleeves, but not /r/yugioh sleeves