Once you run out of toilet paper–and you will–make sure you keep the empty rolls so you can try making fantastic molecular models! Physicist and 3D software engineer Ricky Reusser flattened and linked the cardboard tubes into models of buckminsterfullerene and carbon nanotubes! He's even written a software simulator so you can keep making these even once you've used your toilet paper rolls in place of the toilet paper you can't get. From his guide, Toiletpaperfullerenes and Charmin Nanotubes:
Toilet paper tubes have the curious property that you can flatten them, cut out loops, and link the loops together without fasteners[…]
My brand is regular Trader Joe's toilet paper, though I have no reason to believe anything about the brand is particularly important, beyond consistency—with the exception of those cowards who make tube-free toilet paper rolls. Those won't work. I've considered side-stepping material collection and waiting to buy tag board when shelter-in-place eases, though to be honest, the recycled nature of the raw materials is no small part of what draws me to this project.