Location: Cass is another companion you should come across near the start of the game. She is located at the Mojava Outpost inside of the Mojava Outpost Barracks sitting at the bar drinking.
Info and Quests: You will need to first complete the Side Quest called “Heartache By The Number” to start the process of being able to recruit Cass which will lead you to another, but short, Side Quest called “You Can Depend On Me” from Alice McLafferty. Additional Side Quests may pop up during these Side Quests depending on the choices you choose and how you exactly are playing your game.
As shown at the end of the video, you cannot have more than 1 human companion in this specific group of 6 human companions that you can recruit. You will need to tell whoever may currently be with you, if anyone at all, to head to the Lucky 38 Casino so you can swap with him or her later.
Perk: Whiskey Rose give you and Cass more of a Damage Threshold when you both drink Whiskey. You will also not suffer from Inteligence loss from consuming alcohol and ignore the effects of alcohol addiction. This is great if you want to drink alcohol throughout your playthrough without having any effects from drinking as you would without it.
Upgrade: Hand of Vengeance or Calm Heart.
Hand of Vengeance allows Cass to do 15% more damage with all guns, and allow her to be better with guns. You will need to complete the Side Quest “Heartache by the Number” to get this.
Calm Heart gives Cass +50 Hit Points and allowing her to survive longer in combat.
Location: ED-E is a robotic companion that you can find in the town of Primm. It will be on the table inside of the Nash Residence. Once you repair him, his Side Quest “ED-E My Love” will become available.
Info and Quests: If you did not already know, you can only have 1 human and 1 robotic companion, so if you have Rex following you, as I do in this video, you will need to let him go before you can recruit ED-E.
Once you have recruited ED-E, you can still have Rex as a follower, he can be found at The Kings School of Impersonation back in Freeside where you originally obtained him.
Perk: Enhanced Sensors allow you to detect enemies at an increased range as well as enemies will appear on the compass and can be targeted in VATS even when cloaked. This works even better if you use this along with the Spotter Perk from Craig Boone.
Upgrade: Enhanced Armor or Weapon when you complete the Quest.