Restaurants: - Fast food with drive throughs like McDonald's or Starbucks generally do not expect you to make a purchase to use the restroom. Some you'll need to ask at the register for a key or code, which is intended to prevent drug users from using the bathroom for that - Sit-down restaurants can be hit or miss. Most are understanding, especially if you mention you're a tourist - Malls/food courts typically have public restrooms you can use without buying anything

Gas stations & stores: - Gas stations/convenience stores will require you to ask for a key/code, but generally don't require a purchase. I make a point to thank the cashier/attendant on my way out if I had to speak to them to get into the bathroom - not necessary, but it's a nice gesture - The more upscale truck stops/Sheetz tend to have very clean restrooms and will not require anything for you to get into the restroom - Large retailers like Walmart and Target will likely be public. Some may do the key/code thing, but I've seen it less frequently there than gas stations - Other businesses are a toss-up. Some will have signs saying "no public restroom" which means "buy something and we might let you use it, but probably not". Smaller businesses/strip malls are mostly not worth stopping at.

Misc: - Public libraries! They are usually happy to help!! - Rest stops can be a little sketchy depending on the time of day, and cleanliness varies widely - Parks used to be great, but in the past few years I've found them increasingly closed/locked with no warning or directions to get access. I'm assuming it's also an anti-drug/anti-homeless effort so the bathrooms don't become a liability for folks trying to use them - Fire or police stations can work if you are really, truly, totally desperate. Please be careful where you park so they can still respond to emergencies!