I'm so happy to see this conversation here! Awareness about the damage Plastic waste is causing has become a huge environmental/health issue (research microplastics in the food chain!), so every bit of action we can take in spreading the word helps.
We focus on eco-friendly awareness in my home, so refillable containers are a given in the kitchen & bath. I try my best to buy plastic-free (and it is HARD!), but I do what I can. I also ask guests to not use chemically-scented personal products, so I provide high quality soaps, shampoos, shaving cream, and lotions that guests can use. This is not an area that I worry about "cheap". My attitude is it's better to provide the best you can afford, and charge an extra $ if you need to!
A couple of things I've not seen mentioned: it's the single-use plastic packaging that is one of the hardest things to avoid, so I use a subscription for toilet paper (Who Gives A Crap) Yes, really, that's their name! :D. They have tp, tissues, and paper towels that are all made sustainably using bamboo, and they use NO plastic in packaging or shipping.
I have a pile of fabric and re-usable bags by the front door, and encourage my guests to borrow them if they are going shopping.
We have a whole house filter system, and drinking water is double-filtered. I think this makes guests feel safe about drinking the water, so I rarely find that they are using plastic bottled water. I also have a few stainless steel "go cups" for guests to borrow if they want.
I have a long ways to go, but there are many other little habits I utilize in my home, and I'm currently working on a sheet (or perhaps a little booklet) with eco-friendly tips and recommendations that my guests will be able to use.
Thank you @Paul1255 for starting this thread, and thank you everyone for caring! I look forward to any other tips people might have...