@Jennifer178 @Dee9, so I've started adding in lots of extras to the travel toiletries I provide for guests, e.g. toothbrushes, razors, sewing kits, and a bunch of other stuff, as well as the usual shampoo, shower gel and soap. I've increased the range of teas, coffees etc. and provided them with milk. Sometimes I put a bowl of fruit in the room too.
When they check in, I show them all of this as well as their shelf in the fridge/space in the cupboard. I then politely ask them please to not take other people's food/toiletries without asking, explaining that they may belong to my housemate or another guest who will be upset if someone uses their stuff. I tell them if there is anything extra they would like, including more toiletries, they should ask me and I'd happy to help.
So, they say, no of course we would NEVER take anyone else's stuff! We brought our own toiletries! We're going to eat out/we've just been to the supermarket.
Then what do they do? They help themselves to whatever they like!
Okay, so I'm not talking about every guest, but it seems to be becoming more of a regular thing.