We've toyed around with the idea of prioviding breakfast insofar as providing coffee, tea, instant oatmeal packs, or those new just-add-water pancake/french toast/egg cups. We held back on the food part of that due to the cost. Oatmeal packs are fairly inexpensive, but the microwaveable breakfast cups are substantially more on a per unit basis ($1-2 US each). Thankfully we had a guest who helped us try things out by leaving a large box of instant oatmeal packets in the unit after checkout. We decided to leave them there for future guests. After about 15 or so guests since then, only one packet has been used. I know oatmeal isn't everyone's bag, but that seems like a pretty clear indicator for us that it's probably not worth it.
One other thing that has become abundantly clear to us is that aside from ground coffee, our guests simply will not touch anything that could have been contaminated by another person. We've tried cookies, pretzels, and a few other things that were broken down into a smaller quantity and provided in reusable containers. Every time the guest checked out without ever touching those items.
If it's not individually wrapped, it's a no-go from guests, which naturally drives up the cost, but even at that, we just don't see the demand for breakfast, so we've stayed away from it. We also have a donut shop about 400 yards away from the property. Maybe I'll spend a few bucks and get some things for my next long-term guest, see how it goes, and report back here.