I got the feeling reading your article that you're looking for a simple cost/benefit ratio. Therefore, I think the foray into Newtonian physics (mass, acceleration, gravity) and fluid dynamics (air resistance) isn't necessary. The cost of a given pound is going to be inherently personal and subjective. So, why not just assign some subjective factors to weight and volume and play around with factors? Even if you get a little bit complicated, such as increasing the factors exponentially over a base weight or max weight limit, you'd still be comfortably within 7th grade algebra. Pop a few formulas in Excel and you could investigate your model to no end by adding items and tinkering with the parameters/factors.

On the benefit side of the equation, I'd be tempted to use the exact opposite of the common risk assessment rationale. I'm not an expert in risk management, but I've seen people apply it to projects a few times. They typically apply exponential factors to the probability of an occurrence and the impact of that occurrence and multiply the two to determine the risk factor. In other words, assign 1, 3, or 9 to both the probability and the impact and multiply. E.g. The probability that a Sasquatch emerges from from the woods to flip me off and call me names is very low as is the impact; "Sticks and stones, Bigfoot. Sticks and stones.") Therefore, 1 times 1 = risk factor of 1. Contrast that with a hike through bear country where the probability of encountering a pissed-off bear is high and the impact of that encounter is very high (he kicks my ass). I'd want to mitigate that risk with bells and spray.

To morph risk into your benefit, you could assign the probability of using an item while on tour times the impact of using it or the impact of not having it available. E.g. The probability of using water is very high and the impact of not having it available is very high, ergo, you bring water. The probability of using an electric juicer is low and the impact of not having it available is very low, ergo, you might not be able to justify the cost.

Being a computer nerd, I am interested in this topic. Not because I believe it would yield results any better than gut feel and experience. But interested because it sounds like a fun project and there is a probability that a little surprise pops out of it. Let us know if you pull something together.