I provide English muffins (they're cheap and versatile!), jams, butter, peanut and almond butter, coffee, tea, and half and half for coffee. Sometimes I leave a couple of small orange juices especially if there are kids. If kids are coming, I email ahead to ask if they want milk, and if so, what type since there are so many preferences. I like to leave a few pieces of fruit, but I've stopped doing that since it mostly was left uneaten to spoil.
I also have some basic "famine foods" in the cupboards, e.g. cereals, popcorn, pasta, can of tuna, oatmeal. Things to eat when you've arrived in the middle of the night and the restaurants are closed. I also provide oil, vinegar, spices, hot chocolate mix, and Nutella. Most of it never gets used so I don't have to restock it often. What does go is the coffee (I use Keurig pods... wastefull I know, don't yell at me!), mix of teas including fruit and herbal, and the jams.
I should say I'm within easy walking distance of a decent sized Whole Foods and many restaurants and shops, so people mostly eat out. I should also say that I have a separate unit as part of my house - we do not have to interact, and guests are not sharing my space, so they are not expecting me to cook their breakfast!