Mostly what they call "pack animals", such as mules, burroughs (donkeys), horses and camels. Of course, elephants are great for that type of work too. It largely depends on where your are geographically as to what type of animal is available.
You can't just stack a bunch of stuff on their backs though. Think of putting the load together like a couple of large saddlebags, with straps and padding across their backs and hanging to either side. Load balancing is important too.
Hope this helps,
Animal used for carrying loas is called Beast of Burden