What Yu-Gi-Oh! Cards are a must-have in a warrior’s deck?

It depends in which warrior's deck you are using actually. Like elemental heroes, swordmen, noble knights, etc.

But i recommend those four cards in general :

Silent Swordsman

Lightning Blade

Turret Warrior

Bonus : I highly recommend you to use the last card with this one :

Celtic Guard of Noble Arms

Celtic guard has a powerful ATK points expect he can't attack if you have cards in your hands but there is turret warrior with his special affect he gets celtic attack and add it to his 1200 ATK points so you have a monster with 3300 ATK points which can attack normally.

Source: Quora.com
Credit to: Andrew Lin