Water. Why not just boil the water out of the tap? Also in the camping section of stores you can buy water purifying tablets to have on hand. Also save milk jugs or any beverage container and fill it with your tapwater. Worried about it just sitting there, reboil if it comes to that.
Heck, buying Gatorade is just about the same as buying water in price. Reuse the bottles. At worst you'll have Gatorade for the hot summer months.
Why not buy alcohol and mix 60% alcohol with 40% water? That would cost hardly anything. (in addition to hand sanitizer and soap)
Food. There are so many cheap foods that one could just add water to. Buy bulk multi vitamins to make up for the lack of vitamins in the cheap dried foods.
I'm also sooo not above telling someone to cover their mouth when they cough.I don't care if it pisses them off. I'm also the kind of weirdo that if someone coughs on an isle (many times they don't even have to cough) I will just about pass out from holding my breath as I pass them to get down the isle and breath.
Toilet paper. (obviously buy some) Save your news papers. That stack of old tshirts you were going get rid of, cut them up. At worst they can be shop rags later. Paper towel rolls can be cut in half, literally.
Heres a vid on how to make a DIY mask, There are many more vids on how. I like that they added a plastic shield to cover your eyes.
At this point I'm not ashamed to carry Lysol and spray it when I'm in an Isle at the store. In fact I'm seeing people do it here already.
DIY MASK VIDEO https://youtu.be/aNjpH5lBZ8w