- Ask for your drink without a straw.
- Unplug your microwave when not in use.
- Bring a water bottle to events.
- Stop using air conditioning.
- Choose products that minimize packaging.
I've recently heard people advocate for all of these, generally in the form of "here are small things you can be doing to help the planet." In the EA Facebook group someone asked why we haven't tried to make estimates so we can prioritize among these. Is it more important to reuse containers, or to buy locally made soap?
I think the main reason we haven't put a lot of work into quantifying the impacts of these everyday choices is that they're minor compared to questions like "what should I work on?", "if I'm donating where should the money go?", "how can we figure out the impact of our choices at all reliably?" etc. Quantification, even at a very rough level, is really hard and so we should focus on the most important questions first.
A second reason, however, is that these sorts of activities are often shockingly poor tradeoffs. Perhaps you give up AC to save electricity, but then you get less done during the day, sleep poorly at night, and only save $3/day in electricity and ~$0.75/day in CO2  Or you buy zero-waste laundry paste which you dilute at home, putting money and effort into avoiding a very small amount of plastic packaging. Or you take cold showers and enjoy them dramatically less while slightly reducing your use of heating fuel. Advocacy often explicitly or implicitly treats actions as free, while a full evaluation needs to also consider the cost to yourself.
I'm not saying our personal choices don't matter and that we should give up, but a small number of our choices matter far more than others, and we should put our efforts there.
(Previously: 2015, 2013, 2012.)
 This is figuring 600W average usage for a window unit, which is 14.4kWh/day. Our marginal cost for power is $0.21/kWh, on the high side nationally, so $3/day. Figuring 1T CO2 per kWh, this is ~0.007T CO2/day. Using the same 95th percentile EPA social cost estimate I used in this post, $105/T, that's $0.76/day. These are very rough numbers, but they're enough to see that the costs are low.
I wrote a piece last year about the general version of this problem, which I called the epsilon fallacy: optimizing choices with small impact on the objective, without thinking about opportunity costs or trade-offs.
If we stop doing something that almost all first world humans are doing (say 1 billion people), then our impact will be about a billionth of the size of the problem. Given the size of impact that an effective altruist can hope to have, this tells us why non actions don't have super high utilities in comparison. If there were 100 000 effective altruists (probably an overestimate), This would mean that all effective altruists refraining from doing X, would make the problem 0.01% better. Both how hard it is to refrain, and the impact if you manage it depend on the problem size, all pollution vs plastic straws. Assuming that this change took only 0.01% of the effective altruists time. (10 seconds per day, 4 of which you are asleep for). Clearly this change has to be something as small as avoiding plastic straws, of smaller. Assume linearity in work and reward, the normal assumption being diminishing returns. This makes the payoff equivalent to all effective altruists working full time on solving the problem, and solving it.
Technically, you need to evaluate the marginal value of one more effective altruist. If it was vitally important that someone worked on AI, but you have far more people than you need to do that, and the rest are twiddling their thumbs, get them reusing straws (Actually get them looking for other cause areas, reusing straws only makes sense if you are confidant that no other priority causes exist)
Suppose omega came to you and said that if you started a compostable straw buisness, there was an 0.001% chance of success, by which omega means solving the problem without any externalities. (The straws are the same price, just as easy to use, don't taste funny ect.) Otherwise, the buisness will waste all your time and do nothing.
If this doesn't seem like a promising opportunity for effective altruism, don't bother with reusable straws either. In general the chance of success is 1/( Number of people using plastic straws X Proportion of time wasted avoiding them )
Eyeballing at a EU report chart, it looks like the reduction of carbon output in Europe is mostly due to changes in energy production (in millions of tonns, ca 490 less in 2016 compared to 1990) and manufacturing industries (370 less), but another 650 reduction comes from the little things combined (households, institutions, waste management, agriculture, fuels, industrial processes and product use, commerce, fugitive emissions). So, most of our focus should be on energy, but it does't look overly bad for the small things either. Of cause, if you zoom in on one really small intervention, like refusing straws in drinks, its impact will be very very low... Probably not worth it if it has any cost to you at all.
I'm surprised that you list agriculture and industrial processes under "little things".