Sheets and pillowcases
Changing the sheets after you've been sick is a good thing to do for the obvious reason that you've probably spent an extended time lying there, breathing germs all over the place, sweating out a fever, and generally doing all the gross things that sick people do. The other reason to change your sheets after you've been sick is that getting into a freshly made bed when you begin to feel better sends a psychological signal that you're feeling much, much better.
If your illness is dragging on and you can't muster the energy to strip the bed and launder a full set of sheets, you might want to consider changing the pillowcases as a half-measure. The cases, after all, bear the brunt of your runny nose and sweaty brow. As a bonus, laying your weary head on a clean pillowcase will probably help to make you feel a little less gross.
Did you brave a nasty little cold from the comfort of your couch? There's nothing better than curling up under a comfy throw blanket and festering in front of the TV to binge watch your favorite show. But when you're well enough to get off the couch, don't forget that you just spent three days sneezing into that comfy throw blanket -- toss it in the wash.