Not sure if this is intended, but it seems weird: Bringing along any animals, pack animals or otherwise, in a caravan has no impact on how long the food supply will last, implying that any animals in the caravan simply won't eat anything at all.
Also, similarly not sure if intended or not, but tame alpacas, while they can be brought along on the caravan, don't increase the caravan capacity like muffalos do. It seems like it should be possible to use alpacas as pack animals, considering they are often used that way IRL.
Alpacas aren't pack animals (maybe a bug), and animals will, if they can, just eat the grass. Bring a warg, it'll need food, or travel over ice. For example.