Elephants

[Light a wight tonight]

Sometimes the fact that fAegon has elephants is given as a plus factor, but is that really important? After all, those are warm-climate beasts and Winter is coming. On the other hand, the Wildlings, loosely aligned with Sannis, have mammoths, with giants to ride them. Meseems those should dominate the elephants fairly easily. 

[fenr1s]

These elephants only have very limited military value. The Golden Company doesn't have a huge number of elephants in the first place and even in antiquity the use of war-elephants brought mixed results. On a medieval battlefield with longbows, crossbows and pikemen they shouldn't be effective. They might be useful to build and move siege engines though.

[Lord Corlys Velaryon]

The elephants will likely be what helps the GC break the Reach's cavalry, among other things, Good point on the giants & mammoths, but remembered they didn't exactly hold against Jon & the NW's fire & pitch, nor Stannis' cavalry. Neither are they likely to head south of say Winterfell, let alone the Neck. After the GC defeat the Tyrell forces under Mace or Randyll, yes the elephants likely won't have too much use (besides perhaps siege engines as you suggest) until they are roasted & possibly become food for dragon/s &/or people.