In order to pick up things fast off the ground like plants, mushrooms, loot inside of NPC homes, their dropped weapons and what not all you need to do ishold crouch and spam pick up button.

Default combo is CTRL + spam Left Click

In order to loot containers fast like dead bodies I suggest you to go into ESC>Options>Controls>Custom and find Take All shortcut and change it to something that you find convenient to be pressing for the next couple of dozen hours of gameplay. Something that you can easily reach with your finger and press. For me this is button "T" in this game, it is fairly close to WASD control scheme, also suitable for Take All in meaning