My suggestions come with a caveat: they're going to vary depending on various factors from the type of climate you live in up to and possibly including your medical history.
For instance, elderberry syrup and echinacea tea are frequently recommended because they bolster the immune system. However, if you have any autoimmune disorder, that can make you even sicker.
Keeping a humidifier running is suggested very frequently especially for people who live in dry, cool climates, or high elevations. (And it does help those of us living at nosebleed altitudes!) But it won't work as well for people who live in humid climates.
Some people are allergic to ginger and citrus, which are usually highly recommended even by yours truly.
But in every case I think it's safe to recommend hydration and rest.