Wear comfortable, broken-in footwear. If you feel a hot spot, stop & take off your boots. Put your feet into cold water when you get the chance to cool them.
Wicking inner socks may help prevent blisters.
Bring Leukoplast or Elastoplast bandages, duct tape & any other blister first aid products you like, just in case.
If you do get a blister, using a sterile needle, prick the blister a few times. Drain without touching the fluid or holes. Seal with liquid Betadine and, when dry, place some tape over it. We usually use duct tape it's inexpensive and seems to stay as well as anything else.
Insect Bites & Stings?
Mosquitoes are sometimes a problem though we saw few in September. The Huayhuash is high & windy.
We were lucky on Huayhuash, not bothered by tiny black flies that pestered us elsewhere in Peru in the Cordillera Blanca & near Cuzco. The bite is not painful but the welts get infected causing itching for weeks afterward!
Prevention is the best strategy.
Bring long pants and a long-sleeved shirt. Tuck pants into your socks and shirt into pants. One of our hikers swears by his unlined nylon pants & cycling jacket. Wear gloves.
Insect repellent containing DEET may help
Damage to gear on pack animals
We had a pack damaged when our pack horse rubbed up against rocks. The recommended method of protecting your pack is to cover it with a large burlap rice sack. (This also makes it difficult for curious fingers to open small side pockets.)
You can buy rice sacks in the central market in Huaraz. Make sure the sack is large enough to swallow your whole pack.