I am going to pitch in here against olive oil and (I would add) long-chain, unsaturated oils in general. These are more difficult to digest because they must be broken down before passing through the wall of the small intestine. By contrast, short- and medium-chain fatty acids pass straight to your bloodstream. To get an idea of what an impact this makes, here's a snip from Wikipedia:
"Short- and medium-chain fatty acids are absorbed directly into the blood via intestine capillaries and travel through the portal vein just as other absorbed nutrients do. However, long-chain fatty acids are not directly released into the intestinal capillaries. Instead they are absorbed into the fatty walls of the intestine villi and reassembled again into triglycerides. The triglycerides are coated with cholesterol and protein (protein coat) into a compound called a chylomicron." (https://en.wikipedia.org/wiki/Fatty_acid).
On top of this, fatty-acids in general are superior to other metabolic fuels because of their ATP (energy) density and because they are preferred by critical muscles like the heart and skeletal muscles:
"Fatty acids are important sources of fuel because, when metabolized, they yield large quantities of ATP. Many cell types can use either glucose or fatty acids for this purpose. In particular, heart and skeletal muscle prefer fatty acids." (Ibid.)
Now that we can assume short- and medium-chain fatty acids are the ideal energy source for us (hiking or not, imo), where do we get them?
"Short-chain fatty acids have four to six carbon atoms. These fats are always saturated. Four-carbon butyric acid is found mostly in butterfat from cows, and six-carbon capric acid is found mostly in butterfat from goats. These fatty acids have antimicrobial properties-that is, they protect us from viruses, yeasts and pathogenic bacteria in the gut. They do not need to be acted on by the bile salts but are directly absorbed for quick energy." (articles.mercola.com/sites/articles/archive/2002/08/21/saturated-fat2.aspx)
"Medium-chain fatty acids have eight to twelve carbon atoms and are found mostly in butterfat and the tropical oils. Like the short-chain fatty acids, these fats have antimicrobial properties; are absorbed directly for quick energy; and contribute to the health of the immune system." (Ibid.)
A problem with olive oil (like most vegetable oils) is that its main fatty acid is a long chain fatty acid which must therefore go through a comparatively long, energy intensive process of decomposition and recomposition to provide energy in human metabolism.
Basically the only two plant-based oils with significant amounts of MCFA's or SCFA's are palm *kernel* oil and coconut oil. As for animal sources, butter is the star player since fats such as lard and tallow aren't readily available now, but it is worth noting that beef pemmican (which is mostly beef tallow) was a prized staple among the American frontiersmen. It's not particularly easy to acquire now, but it's an excellent trail food.
Another factor to consider is the saturation of fatty acids. Saturated fats have no double bonds between carbon atoms, so they are "saturated" with hydrogen. This makes them more calorie-dense than mono- or poly-unsaturated fats.
In addition, polyunsaturated fats are more prone to rancidity both in the air and in the human gut and blood where oxygen is also present due to respiration. Here's a concise explanation:
"Unsaturation means that some hydrogen atoms have been removed, and this opens the structure of the molecule in a way that makes it susceptible to attack by free radicals. ... When the oils are stored in our tissues, they are much warmer, and more directly exposed to oxygen, than they would be in the seeds, and so their tendency to oxidize is very great. These oxidative processes can damage enzymes and other parts of cells, and especially their ability to produce energy." (coconutoil.com/ray_peat_unsaturated_oils/)
Next, there is the problem of enzymes.
"To defend the seeds from the animals that would eat them, the oils block the digestive enzymes in the animals’ stomachs." (ibid.)
Besides being typically associated with enzyme inhibitors, unsaturated oils require additional enzymes in order to break the double bonds that distinguish them from saturated fats.
"β-Oxidation of unsaturated fatty acids poses a problem since the location of a cis bond can prevent the formation of a trans-Δ2 bond. These situations are handled by an additional two enzymes, Enoyl CoA isomerase or 2,4 Dienoyl CoA reductase." (Wikipedia, "Fatty Acid Metabolism").
beta-oxidation is the process by which we get energy from fatty acids, and the "cis" bond is the chemical structure which distinguishes unsaturated from saturated fats.
Having said all that, we cannot help wondering what the foods lowest in unsaturated and highest in saturated fats are. Fortunately, there are lists for this sort of thing. In one following, "PUFA" means "Poly-Unsaturated Fatty Acid" and "SAFA" stands-for "SAturated Fatty Acid":
Butter (4% PUFA, 50% SAFA)
Ghee (4% PUFA, 48% SAFA, 2% cholesterol)
Cocoa Butter (3% PUFA, 60% SAFA)
Coconut oil (2-3% PUFA, 92% SAFA, 0% cholesterol)
Palm kernel oil (2% PUFA, 82% SAFA)
As a final note: I always cringe when I see people posting about eating starchy carbs and/or sugary fruits with their fats. This is a recipe for prolonged, energy-sapping digestive malease.
"Dietary carbohydrates (sugar) stimulate the release of insulin which inhibits the breakdown of lipids (fats and oils) for energy and directs them towards metabolic pathways for storage as FAT." (http://newton.dep.anl.gov/askasci/mole00/mole00423.htm)
Unless you are willing to suck down melted butter or coconut oil by the quart (hint: don't), you *will* need to dilute your fatty acid goodness with *something*. I recommend protein powders (e.g., pea, rice, or hemp), lecithin powder (preferably sunflower), and possibly some low-carb nut or seed meal/flour (e.g., coconut flour, almond flour, flax meal, etc.) and, if you feel adventurous, low-carb green "superfood" powders (e.g., chlorella, spirulina, wheat grass, and derivative blends thereof).
Keep in mind that it's easy to overdo nuts and seeds. These have high concentrations of unsaturated, long-chain fatty acids which will clog your metabolism and sap your strength. However, they *are* a step up from high-starch fillers like oatmeal, peanuts (which are legumes, not genuine nuts), and potatoes which completely lay waste to your insulin pathways and leave your precious oils sitting in your gut and fat tissue unused.