I have a holiday let except it's our own home that we move out of during the summer. A bugger to move all our stuff out, but it does mean that the place looks very homely and not sterile and that the kitchen is fully stocked with absolutely everything. If I can cook a Christmas dinner for 8+ people there, then you're all set for summer meals!
I leave 3 toilet rolls per WC, it's self-catering so no I'm not buying enough toilet paper for your entire stay, but you'll get more than enough to last you a good few days. I do this no matter how many people are staying in the house, so if there are only 3 of you then you're getting 9 toilet rolls for a week. I also leave coffee pads, a massive box of different teas, fancy Pukka teas, olive oil/salt/pepper/spices/herbs, enough dishwasher tablets for one machine run per day plus a couple extra, a big bottle of washing detergent, a small pack of bin bags, a full cleaning kit, hoover, mop etc, the works. In my welcome pack, I also do 2 bottles of local wine, a local lemonade, some beer, some nuts, crisps and olives. I also leave big bottles of local artisanal shower gel in each shower.
Overall, no one has taken anything, not anything I've noticed. Before the summer I clear the bookcase of any books that I'd be sad to be stolen just in case people do exchange books whilst there. Same with anything else I'd be sad to see go.
The biggest thing for us is that people move furniture around, which I find really strange. We have a large outdoor dining table in the garden and another large one that's extendable in the veranda, but for some reason one group decided to take the heaviest dining table from our lounge into the garden! No clue why, makes me chuckle to this day.
We have cupboards in the utility room that are locked and have "private" stickers on where we keep our personal belongings and the amount of people who try to break them open/have a nose is honestly ridiculous. You're not finding anything in there other than my winter clothes, slippers and the roller blades I've never used!!