Don't forget that many foods were stored in the days before refrigeration. If you use those foods that kept well then, they'll be good today. Consider buying a dehydrator if you tend to go on a lot of long trips. Dehydrated food can keep a long time.
- Before leaving home, paint the egg shells with vegetable oil to prevent oxidation of the egg and spoilage. Eggs will keep if cool in this condition for at least a week. Store in a rigid plastic egg container (available at camping stores) at the bottom of the kayak (where the water will keep it cool) and make sure that light, insulated gear (like clothing or a sleeping bag) is above it.
- The harder and drier the cheese, the better it will keep without refrigeration. Vacuum packaging is a good way to avoid some spoilage, as it keeps air off of the cheese. Forget mozzarella and camembert - look for parmagiana (parmesan; in a block - bring a small grater; the pre-grated stuff is bulkier), emmental, cheddar etc.
- You really can't get butter to keep. However, there are some good substitutes for butter. If you live in a multi-cultural metropolitan area, look for Ghee in an Indian shop or even a large supermarket. Ghee is clarified butter and will keep without refrigeration as long as you keep it cool (like in the bottom of your kayak on the water). You can also use vegetable oils in place of butter for many tasks and in baking, you can use lard instead of butter - lard can keep in a cool place without refrigeration. Before you head out, check with Joy of Cooking or another good cookbook on how much of one thing substitutes for butter. For example, only 7/8 as much lard as butter is required.
- Cooked meats that have been dried can keep well. You can dehydrate cooked hamburger with success. Make sure that you use very lean meat - the fat can go rancid. Sausages and similar meats will survive without refrigeration as well - summer sausage is sold in non-refrigeration packaging. Vacuum-packed, sliced prepared meats will keep for several days as well. Canned meats are an obvious choice - avoid Spam, as it apparently does not actually contain any real meat :-) Hams, corned beef and other meats are available in cans.
- Dried, powdered milk is not bad - it is compact and just has to be mixed in water to get milk. Skim milk powder is common, but whole and partially skimmed milk may have a better taste - these are available in some health food stores. Sterilized milk is sold in tetrapak boxes. You can find one liter and little quarter liter boxes in most supermarkets. An alternative to milk is soy milk. This is also sold in tetrapaks and is available in plain, vanilla and chocolate. If you like milk, but not soy, try the vanilla soy - it's a tolerable milk substitute.
- Hard root vegetables are great - carrots, potatoes and similar will keep well. Softer fruits and veggies are suitable for dehydrating - tomatoes, apples, etc are a real treat. Some can be purchased dried at bulk food stores or supermarkets. Sun-dried tomatoes are often available and add a kick to pasta dishes or any other meal. Leafy vegetables are a problem - forget about lettuce except for very short trips - heat and banging around ruin lettuce in short order.