Stiff brush. I get 'em from the dollar store so I don't feel bad about throwing them away when they get gunky or torn up. A dollar store toilet brush works fine for gunky drivetrains, hubs, spokes, etc. Sometimes they carry smaller stiff bristled plastic utility brushes so I'll buy a few when they get 'em.

Cheap shoelaces to clean between the cogs on freewheels/cassettes. I moisten the laces slightly with a bit of goo remover, WD40, whatever's handy. Works like dental floss. Flat cotton laces get snagged and torn up after a few uses but are cheap so I discard them after a few uses. Braided laces last longer and don't snag as easily on the teeth, but need to be cleaned occasionally.