Pack Rat

Pack Rat is a perk in Fallout 2, Fallout: New Vegas, Fallout 76 and Fallout Tactics.

Effects
This perk increases one's carry weight by 50 lbs.

You are efficient at arranging your inventory in general. This makes it much easier to carry that little extra you've always needed. This is useful for characters with low Strength, i.e. sharpshooters and mediators.

Its usefulness is reduced in Fallout 2 with the addition of larger teams of traveling companions and the Highwayman's trunk.

Effects
This perk halves the carry weight of items that have a carry weight of 2 or less. All affected items in the game world will display their new lowered weight.

In hardcore mode, this applies to ammunition weight, which could cause this perk to be especially useful, allowing you to carry twice as much ammunition at the same weight.

Bugs
There appears to be a bug related to Pack Rat in that due to the discrepancy between a follower's weight and the Courier's weight. The Courier is capable of adding an unlimited amount of ammunition into their companion's inventory despite the fact that it will exceed the companion's max weight i.e. 30,000 rounds of 5mm ammunition can be added if the companion starts out with room to carry an extra round, and the courier deposits the rounds in small amounts at a time.