In addition to those mentioned above, there are few other items I would also suggest bringing along. They are basic requirements in the United States Special Forces Training Phases I, II, & IV.
A protractor. It is extremly difficult to terrain associate on a map if you are in an area without many prominent landmarks. Using the compass and the protractor you would be able to re-section off of any landmarks on the map (given there are at least two) and determine your location.
If you do not know how to use a compass, or protractor, and have no idea how to read a map, get a GPS system with spare batteries if you are going to be screwing around in places you could get lost. Plot your starting point as somewhere with water and medical facilities, and other points with water or shelter as you may find them in your trek. It only takes a moment to annotate a rally point, and it is better to have it and not need it...
Bug Juice, or Insect Repellent if you prefer the politically correct nomenclature. There is nothing so pesteringly itchy, except for a dose of the clap, than a bug bite behind your elbow or on your earlobe.
And I tend to disagree with not bringing salty food. Salt contains electrolytes and helps you retain water. It is also inexpensive. There are packets you may be able to purchase at Army Surplus stores called ORS. Oral Rehydration Salts. You mix these into a one quart canteen and sip it slowly on your trek and you most likely won't go down as a heat casualty. It does taste like diaper squeezings though.
I myself try to consume a mouthful of water every seven to ten minutes. This keeps you well hydrated and stops you from urinating too much, which dehydrates you quickly. If you consume a whole canteen every time you stop to drink, you are just pissing your water supply away.
Hydrate yourself thoroughly the night before you leave for your hike. Two or three quarts of water prior to strenuous activity will not hurt you at all.