Minimizing leaks will depend on the air bubble inside the bottle. Let's assume that you have an 8-ounce bottle with 7 ounces of liquid and 1 ounce of air bubble inside, and that you cap it at sea level. Then if you take it up to 10,000 feet elevation, the air pressure outside is reduced, so the air bubble tries to leak out of the cap. Taking it the other way around, assume that you have the same contents and that you cap it at 10,000 feet elevation. Then if you take it down to sea level, the air pressure outside is increased, and that squeezes on the bottle, trying to force the liquid out of the cap. You can minimize that problem by squeezing the air bubble out before you tighten the cap, but you can go only so far with that unless you use a Platypus-style container.