I've seen a bit to the contrary on here, BUT, I think the Pack Rat Perk is pretty Overpowered.

I took Strong back and Pack Rat thinking that it would be an extra 100 weight extra on the things I scavenge most...
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What I found out is that Pack Rat doesn't even need Strong Back to back it up.
Unlike Strong Back, Pack Rat works for your companions as well. Half weight all around.
And it makes some inventory weigh next to nothing (In Fact, Coyote Tobacco does weigh nothing now)
And for you hardcoe gun toters, that's double the ammo for the same weight cost.
I didn't even need to make a run to Goodsprings for a stock drop off for over 5 hours of gameplay

This perk went from a "erm, I dunno" to a No Brainer in .02 seconds flat.