I've set up around 20 vacation rentals at this point and order almost everything on Amazon, including most furniture (Wayfair is also good for furniture). I can save a few bucks on my kitchen outfitting list by shopping Walmart isles, but I prefer the convenience of clicking a button.
We add coffee bars to each rental and guests love it. I get a Keurig, k-cup carousel, and two small bowls. We stock the carousel with k-cups and the bowls with sugars and creamers (all of which I order on Amazon).
I highly recommend stocking disposable makeup removal wipes. We finally started doing this after 2 years of replacing probably hundreds of white towels, and the stains have nearly stopped completely.
Another nifty item I've been putting in all of our rentals is bedroom lamps with USB plug-ins in the base, like you find in hotels. Guests don't have to pull the bed out to find the wall sockets, they just plug their phone right into the lamp.
For bedding, get a duvet with two sets of covers. Rotate your covers each turnover with the rest of your linens. It's much easier to replace a stained $30 duvet cover than a $100 comforter. Don't forget mattress protectors!
Recently I began finding sofas secondhand and saving a lot of $. At first I was against the idea of secondhand furniture and tried ordering sofas online, but 100% of them were horribly uncomfortable. I've been finding very gently used and stylish sofas for $150 or less.