For pure calorific content, you cant beat Kendall Mint Cake.
Its basically glucose, sugar and some mint essence, stores very well, is light, cheap and you can even make some yourself easily enough. There's a reason Edmund Hillary took it to Everest :-)
Id also take lots of beef jerky, which is great protein for the weight.
Various flavours and substitutes exist such as turkey jerky. I had fish and squid jerky in ukraine recently, and they were great alternatives too.
Many people are suggesting canned goods, but I dont think Id want to be lugging these about personally, they're very heavy for what is essentially 1 can = 1 meal.
You mentioned finding water in the woods is easy, compared to finding food. That would make me think one of the best things you can take is a fishing rod, or maybe even a net. You could set this up in a river overnight and build a basic funnel/box from sticks. Even if it only worked on 2 nights, it would still be worth packing compared to 2 days food.
You could also spend some time reading up on various berries, plants and nuts growing in the woods. There are quite a few that are easy to identify, but obviously there are also some which are poisonous or best left to the experts to identify.
Finally Id want to be taking a lot of grains. Quinoa would be my choice, along with a few bags of herbs and spices (salt and pepper essential, garlic powder etc). These can make even the most boring meal a lot more tolerable.