One bottle on each kitchen counter beside the Dawn here, Paul, and a spare bottle in each laundry room on the shelf with the detergent. 

., laundry detergent, dish detergent, paper towels, etc.

I have a shelf in the laundry room where they can leave laundry detergent and softener, but it's at their own risk and I'm not responsible if someone steals or uses it.

The only other things I would remember to factor in is the initial cost of furnishing the unit (obviously completely filling a unit with everything from a couch to TV to plates and cups and linens isn't cheap at the get-go.) and then the costs of expendables (toilet paper, paper towels, dishwashing detergent, cleaning supplies, etc.)

I poured a few bottles of Dawn dish detergent over the next 12 months and watered it in until grass finally began to grow back.I did all the work myself (except the new 200 Amp service) over a fourteen month period, including painting inside and outside.

@Matt ClarkI replace my coffee, creamer, and laundry detergent the most because I offer it for free.

This is the one i bought PowerBoss Gas Pressure Washer 3300 PSI 2.5 GPM Powered by HONDA GX200 with 30’ EASYFlex High-Pressure Hose, 5 Nozzles & Detergent Injection

If you go for new ones educate your tenants to use less detergent or you will end up with useless service calls-don't ask how I know!

We’re quickly realizing that our trips to Walmart for consumable supplies (toilet paper, paper towels, dish detergent, etc) are becoming far too frequent.For the people that have multiple units, what is your strategy for buying and storing these supplies?  

Skimp on light bulbs, laundry detergent and paper towels.