Send all your eco-inquiries to Jennifer Grayson at eco.etiquette@gmail.com. Questions may be edited for length and clarity.
Every summer our dear but not-at-all eco friends come to stay with us; every year we're left dealing with the waste that's left in their wake. They ask us to buy junk food snacks, they want to order take-out every night (all those containers!), and I spend the whole week fishing their recyclables out of the trash. Oh, and they only drink bottled water and always complain about our scratchy (recycled) toilet paper...
-Alexa
What is this, a house or a Hilton? Maybe this year, you should add tags to their bottles of water like the hotels do, stating there will be a $5 charge added to their room for each one consumed. See if that'll deter 'em.
Seriously, though, I would conveniently "forget" about buying the bottled water this year. Just make sure the house is stocked with snacks and other necessities any reasonable house guest would expect. If your friends request a Fiji upon their arrival, just say something like, "Oh, John and I got this great water filter so we don't have to buy bottled water anymore. I was feeling so guilty about all that plastic trash that's collecting in the ocean. Have you heard it's like a floating landfill the size of Texas?"
If, after that, they still want to go out and buy their own bottled water, well, you're just going to have to suck it up and make sure all the empties go in the recycling bin.
But with the biggest eco offender likely out of the way (a week's worth of plastic water bottles), I would take a deep breath about the rest. When you consider the fuel emissions of the flight I'm guessing your guests took to visit you, a bag or two of Doritos pales in comparison. (And seriously, organic corn chips come packaged in plastic, too.) You don't want to be so overzealous in your quest for eco-righteousness that your guests feel unwelcome.
Consider the case of my red-blooded Southern cousins, who came to California for a visit with their longtime foodie friends, only to discover upon their arrival that the friends had become strict vegans. Now, this would have been fine had the friends been willing to compromise and go out for a few meals where everyone could order something to make them happy, but no: The friends insisted on preparing every meal at home, trying to convert their guests to a vegan diet, too.
"It was interesting to see how they prepared all this food, and some of it was delicious, but two days in we were absolutely starving," said my cousin. If the hosts' goal was to make sure their friends wouldn't be back for another visit anytime soon, they accomplished it.
If your aim is to enjoy your friends' company rather than count their carbon emissions, then loosen up and compromise where you can: Order takeout from a place you know uses compostable, not Styrofoam containers; label your recycling, compost, and trash bins so it's clear which is which (and nicely explain the difference); and buy them a pack of the softest recycled toilet paper you can find (I like Seventh Generation).
Remember, too, that no house guest is perfect, hence wise Ben Franklin's aphorism about fish and visitors. Even guests who are acutely aware of their hosts' eco inclinations can misstep: Take my mother-in-law, who likes to throw used paper towel in the recycling bin when she comes to visit (composting only!). But forever-trying-to-please love that she is, she also always treats us to ridiculously expensive local pastured steaks from the best butcher in town. (I append our microfiber cloths with a roll of paper towel for her visits and do eat sustainably raised beef on occasion, in case you're wondering. See? Compromise!)
Which brings me to my final point: One of the reasons my MIL knows about the grass-fed butcher is because while I try not to preach green while she's visiting, I do feel free to introduce her to some cool stuff that just so happens to be sustainable. As you should do with your guests: Go shopping for dinner together at the farmers market; take them on a beautiful hike by the river; serve up some wine from a growler filled at your local winery.
If your guests are shrugging after the farmers market and still tossing cans of Diet Coke in the trash, then pour yourself a big glass of that local vino and slap on a smile. You can scrub your house with Dr. Bronner's and vinegar from top to bottom when they're gone.