1. A pocket knife. This is a very valuable tool to build up a shelter, help you with your food and even to fabricate new tools, so a durable, reliable pocket knife will be your best friend if things turn wrong.
2. First aid kit. From simple cuts up to snake bites and even accidental gun injuries, you might face all kind of medical situations on the field, so be sure to include a first aid kit complete enough to deal with the commonest situations. On this regard, be sure to include gauze sponges, antiseptics, pain killers, antihistamines and a couple of adrenaline shots in case of severe allergic reactions; additionally you must keep on your first aid kit an extra supply of your regular medicines, just in case the trip extends more than expected.