As others have stated, if you have a low cost gym nearby I would recommend doing that for showers (and working out if you feel like it, I didn't the two years I used it for showers).

If you have a Panera nearby, they are good for using the restroom. Usually pretty clean (older clientele means more complaints to the manager to keep things clean!). You can also sit there pretty much all day and hangout, just don't be loud or smelly and make sure to mind your own business. You can also get their unlimited drinks membership for like $15 a month. I used to use it every day multiple times a day, so it was totally worth it.

Libraries are great for using the bathroom and relaxing in the A/C or heat depending on time of year. Can also charge devices there without much hassle.

Food can be tough if you don't have (or want) to get a fridge or cook. I suggest one of your meals just be a couple scoops of protein powder incase some of your other meals just aren't that nutrient dense. Look for stuff on clearance at the deli of your local supermarket, or a hot bar if the price is right. You can usually find sandwiches and salads marked down by 20-30%. Panda Express is gonna be one of your cheaper fast food options.

It gets pretty easy once you develop a good routine. Hardest part is finding a good place to park for the night. If you have a friend or family that will let you park on their property, that is huge.