Take a personal supply of Protein / meal replacement bars with you. I always have enough to be able to have two per day. There are no places to purchase food once out of the major cities. You may find a small "bodega" in some of the villages were you can get a few things like salt, rice and beans. We always buy food to prepare while in the city and take it along with us. There are lots of grocery stores in Iquitos somewhat smaller but similar as in the US.

Fish are usually abundant everywhere you go. You can at least get a few piranha if you wish. A fishing pole would come in handy but we have caught them on a handline before.

Monkey tastes like pork but it will gross you out when its on the fire. Its like cooking a human baby. Even watching the locals nibble the meat off from between the fingers is more that most can handle.