Say, you have extra cash and want to invest in some medical apparatus for your home. Aside from having a First-Aid Kit and thermometer (digital ear if there are babies/kids), two other things that I think are good investments are a humidifier/nebulizer and a blood pressure monitor.
Humidifiers or nebulizers can help with colds or allergy attacks. Plus, they're easier to do than steam inhalate, which poses a great risk of scalding especially when the sick one in question is a bucking child.
A BP monitor, on the other hand, will come in handy if you're regularly exercising, are pregnant, are obese, or have a history of heart/cholesterol problems in the family. They're also advisable to have around for people in their 40s, since tendencies for hypertension increase around this time.