I'm in a campaign where our party are spying on and trying to retrieve relics from Thay. I have a raven familiar and I was planning to use it for sending reports back to Waterdeep. (We are only level 2 so we don't have access to travel spells.)
The thought came to me to also use this bird to send cash back for magic items to be bought out of Thay. According to the Carrying Capacity it could carry it, but I'm not sure if carrying a Handy Haversack (5 lbs.) would be possible, because I have no idea how flight and carrying capacity work together.
Best Answer
From the rules on movement modes:
Unlike walking, there's no rule that lets you move slower with higher loads; if you exceed light load, you just can't fly. If you need a more explicit prohibition rather than mere lack of permission, consider the feat Reinforced Wings from Races of the Dragon, which says:
Now, a raven has Strength 1 and is Tiny. Being a familiar doesn't change either of those properties. So look that up on the carrying capacity chart, which says that Str 1 has a light load of "3 lb. or less", and Tiny multiplies that by ½.
Conclusion: your raven can carry at most 1.5 pounds while flying.
Even if carrying capacity weren't a problem, the distance from Thay to Waterdeep is about 2400 miles. A raven's 40 ft. base speed translates to overland travel of 32 miles per day. So a round trip would take 5 months.